Here's the CONFIG block for one of the instances on my laptop:
DBCC TRACEON (3604);
DBCC CONFIG;
GO
CONFIG:
DS_CONFIG @0x00000000043A3060
cconfsz = 8                          cmajor = 9                           cminor = 0
crevision = 76                       cbootsource = 2                      crecinterval = 0
ccatalogupdates = 0                  cmbSrvMemMin = 16                    cmbSrvMemMax = 2147483647
cusrconnections = 0                  cnetworkpcksize = 4096               ckbIndexMem = 0
cfillfactor = 0                      ctapreten = 0                        cwritestatus = 0
cfgpriorityboost = 0×0               cfgexposeadvparm = 0×1               cfglogintime = 20
cfgpss = 0                           cfgpad = 4096                        cfgxdes = 16
cfgaffinitymask = 0                  cfgaffinitymask64 = 0                cfgIOAffinityMask = 0
cfgIOAffinity64Mask = 0              cfgbuf = 4362                        cfgdes = 0
cfglocks = 0                         cfgquerytime = 600                   cfgcursorthrsh = -1
cfgrmttimeout = 10                   cfg_dtc_rpcs = 0                     cclkrate = 31250
cfg_max_text_repl_size = 65536       cfgupddate = 41023                   cfgupdtime = 14252889fRemoteAccess = 1                    cfgbufminfree = 331                  cnestedtriggers = 0×1
cdeflang = 0                         cfgTransformNoiseWords = 0×0         cfgPrecomputeRank = 0×0
crossdbownchain = 0                  cidCfg = 0x3400d008                  cidCfgOld = 0x3400d008
cfgCutoffYear = 2049                 cfgLangNeutralFT = 1033              maxworkthreads = 0
minworkthreads = 32                  minnetworkthreads = 32               threadtimeout = 15
connectsperthread = 0                cusroptions = 0                      exchcostthreshold = 5
maxdop = 1                           cpwdpolicyupgrade = 0×1              cfServerTriggerRecursion = 1
cfDisableResultsetsFromTriggers = 0  cfgPHConnectTimeout = 60             CLREnabled = 0
cfgmaxcrawlrange = 4                 ftSmallBufMin = 0                    ftSmallBufMax = 100
ftLargeBufMin = 0                    ftLargeBufMax = 100                  RemoteDacEnabled = 0
CommCritComplianceEnabled = 0        EkmEnabled = 0                       cUserInstanceTimeout = 0x3c
cfgEnableUserInstances = 0×1         m_BackupCompressionDefault = 0×0     FilestreamAccessLevel = 2
OptimizeForAdhocWorkloads = 0        cchecksum = 1191                   
DBCC execution completed. If DBCC printed error messages, contact your system administrator.
The two highlighted fields are the time the sp_configure options were last updated. The cfgupddate is the day that sp_configure was last updated and the cfgupdtime is the time on that day is was last updated. Here's how to interpret them:
  • cfgupdtime is the number of 3.3ms intervals since midnight. 14252889 x 3.3ms = 47034533.7ms = 47034s. 47036 div 3600 (secs/hour) = 13 hours. And (47036 mod 3600) div 60 (mins/hour) = 3 mins. And (47036 mod 3600) – (3 x 60) = 56 secs. I last updated my sp_configure settings at 13:03:56 when I tested it by setting MAXDOP to 1.
  • cfgupddate is more complex. It's the number of days since January 1st, 1900. Doing a raw 41023 / 365 = 112.391blah. So 112 years, leaving 41023 – (112 * 365) = 143 days over. but we also have to account for the extra day in all the leap years since 1900. 1900 itself isn't a leap year, but 2000 is, plus 24 between 1900 and 2000, and 2 since 2000, not including this year. So we have 143 – 1 – 24 - 2 = 116 days. 116 – 31 (Jan) – 29 (Feb) – 31 (Mar) = 25. But it's the number of days *since* January 1st, 1900 so we add 1 and we get 26 – and today's the 26th of April.
I last changed the sp_configure options at 13:03:56 on April 26, 2012. Its trivial to come up with T-SQL code to do all of this, using the WITH TABLERESULTS option of DBCC PAGE.
Note the time of the last sp_configure change is only flushed to the CONFIG blocck on disk when the server restarts, is recollated, or some other major change occurs. This means that if you make a change, the time returned by the code will not change. You can prove this to your self by making a change, waiting an hour, rebooting, and running the script. The time returned will be the change time, not the reboot time.
[Edit 4/30/12: I fixed a small arithmetic bug in my milliseconds calculation thanks to Nils Gustav Stråbø.]
You can download the code from SQLskillsSPConfigureChanged.zip (1.50 kb)
If you want to figue out *what* changed and you don't have error logs available, you'll have to restore previous backups of master (you're backing it up every night, right?) and compare the CONFIG blocks.
Hope this is useful (or at least interesting!) to some of you. Better go set MAXDOP back to zero before I forget…
The code to do this is below (I'm sure someone will comment on a cleverer way to do some of this):
/*============================================================================
   File: SQLskillsSPConfigureChanged.sql
   Summary: This script reports the time that sp_configure options were
   last changed
   SQL Server Versions:
         2005 RTM onwards
——————————————————————————
  Written by Paul S. Randal, SQLskills.com

  (c) 2011, SQLskills.com. All rights reserved.
  For more scripts and sample code, check out
    http://www.SQLskills.com
  You may alter this code for your own *non-commercial* purposes. You may
  republish altered code as long as you include this copyright and give due
  credit, but you must obtain prior permission before blogging this code.

  THIS CODE AND INFORMATION ARE PROVIDED "AS IS" WITHOUT WARRANTY OF
  ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED
  TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A
  PARTICULAR PURPOSE.
============================================================================*/

SET NOCOUNT ON;
– Create the temp table
–
IF EXISTS (SELECT * FROM msdb.sys.objects WHERE NAME = 'SQLskillsDBCCPage')
DROP TABLE msdb.dbo.SQLskillsDBCCPage;
CREATE TABLE msdb.dbo.SQLskillsDBCCPage (
    [ParentObject] VARCHAR (100),
    [Object]       VARCHAR (100),
    [Field]        VARCHAR (100),
    [VALUE]        VARCHAR (100));
DECLARE @hours   INT;
DECLARE @minutes  INT;
DECLARE @seconds  INT;
DECLARE @milliseconds BIGINT;
DECLARE @LastUpdateTime DATETIME;
DECLARE @upddate  INT;
DECLARE @updtime  BIGINT;
DECLARE @dbccPageString VARCHAR (200);
– Build the dynamic SQL
–
SELECT @dbccPageString = 'DBCC PAGE (master, 1, 10, 3) WITH TABLERESULTS, NO_INFOMSGS';
– Empty out the temp table and insert into it again
–
INSERT INTO msdb.dbo.SQLskillsDBCCPage EXEC (@dbccPageString);
SELECT @updtime = [VALUE] FROM msdb.dbo.SQLskillsDBCCPage
WHERE [Field] = 'cfgupdtime';
SELECT @upddate = [VALUE] FROM msdb.dbo.SQLskillsDBCCPage
WHERE [Field] = 'cfgupddate';
– Convert updtime to seconds
SELECT @milliseconds = CONVERT (INT, CONVERT (FLOAT, @updtime) * (3 + 1.0/3))
SELECT @updtime = @milliseconds / 1000;
– Pull out hours, minutes, seconds, milliseconds
SELECT @hours = @updtime / 3600;
SELECT @minutes = (@updtime % 3600) / 60;
SELECT @seconds = @updtime – (@hours * 3600) – (@minutes * 60);
– Calculate number of milliseconds
SELECT @milliseconds = @milliseconds -
 @seconds * 1000 -
 @minutes * 60 * 1000 -
 @hours * 3600 * 1000;

– No messy conversion code required for the date as SQL Server can do it for us
SELECT @LastUpdateTime = DATEADD (DAY, @upddate, '1900-01-01');
– And add in the hours, minutes, seconds, and milliseconds
– There are nicer functions to do this but they don't work in 2005/2008
SELECT @LastUpdateTime = DATEADD (HOUR, @hours, @LastUpdateTime);
SELECT @LastUpdateTime = DATEADD (MINUTE, @minutes, @LastUpdateTime);
SELECT @LastUpdateTime = DATEADD (SECOND, @seconds, @LastUpdateTime);
SELECT @LastUpdateTime = DATEADD (MILLISECOND, @milliseconds, @LastUpdateTime);
SELECT @LastUpdateTime AS 'sp_configure options last updated';
– Clean up
–
DROP TABLE msdb.dbo.SQLskillsDBCCPage;
GO