Did you test your software against SQL2008? There were some T-SQL changes on SQL2008 and deprecated features. You need to ensure your T-SQL code behind will also work or was changed accordingly.

A useful link:

http://msdn.microsoft.com/en-us/library/ms143532(v=sql.100).aspx

I actually remember few years ago, when I helped with an in-place upgrade, an old MS style join got broken in the code. I do not remember if it was when moving from 2000 to 2005 or 2005 to 2008. Long story short, the code was not tested by the developers and those joins stopped working.