The compatibility level of 80, was from SQL 2000, 90 is 2005. Features introduced with SQL Server 2005 probably wont work, I assume this based on trying customised reports and trying to use pivot in a query, neither of these work unless the compatibility level is altered to 90. From this I expect none of the 2005 introduced features will work, but if the database doesn't need them you don't need to worry.
I don't know of any performance gains I expect you'd have to test that.
Facts are stubborn things, but statistics are more pliable - Mark Twain
Carolyn
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