João Paulo was investigating Guid performance when used as identifiers in a SQL Compact database and discovered that the performance of Guid.NewGuid() left a lot to be desired. The reason for this is that the function uses lowest-common-denominator support, using a random number generator and setting a couple of specific bits to conform to guid standards. Another method I’ve been recommending for some time is to use the native CoCreateGuid() function – see http://www.peterfoot.net/NeedAGUIDInAHurry.aspx. This method is supported in all devices running Windows Mobile 2003 and above, and in Windows CE 4.x. I’ve been using it in the InTheHand.Guid2 class in Mobile In The Hand (Will be renamed to GuidHelper in the next version). I did some tests creating 100,000 guids in a row with both methods. Guid.NewGuid() took 139 seconds, and GuidHelper.NewGuid() took a mere 9 seconds. As you can see that is quite a significant difference.