Right, I've seen it mentioned on here as well, but we use GUID COMBs as well (a GUID which has as it's basis a stamp in time). We have one FUNCTION in the database and all our "ID" columns use this function to derive their primary key in stead of "NEWID()" or "NEWSEQUENTIALID()". In the code, the same is done so we don't have to hit the database. A "helper" or utility class was created so we can just say "SomeObject.ID = DataUtility.NewSequentialID()". We couldn't do it with .NET Extension methods because extension methods rely on a instance already being created in order to pick up their intellisense (ex. this makes no sense to do: Guid.NewGuid().NewSequentialID()). So a static class/method was used.

So, don't reinvent the wheel in this case, the GUID COMBs work great! I've also been able to insert millions of rows using that function and it was fast! Also, there is little to no fragmentation in the database because these ARE sequential IDs.