A common question from customers; should we apply SP2 or wait.
There is no Golden answer; I would suggest:
a. Test the application in testing / staging environment first
b. Compare the performance against baseline
c. Refer to wonderful blog article from SQL PSS team - that explains the details about the re-release of SQL Server 2005 SP2 and post release fixes.
I would say this is a must read for anyone deploying SQL Server 2005 SP2 to understand the various hot fixes, GDRs and procedures.
From typical DBA perspective I would recommend check