I'm currently working on a 2000 to 2005 conversion myself. The biggest thing I have found is that the stored procedures that the vendor wrote do not fully adhere to ANSI standards. For example, I am having to re-write portions of these procs to remove *= and =* in favor of OUTER JOIN. The unfortunate thing is that simply importing the database to 2005 and changing the compatibility mode to 90 won't tell you of these types of problems. You won't know there is a problem until you try to run the proc the first time.