I recently applied Service Pack 3 for SQL2005 64 bit and my server performance has been very slow since. The statistics have been updated on my databases, but that has not improved query performance.
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I've gotta agree with hmscott... you may have other issues that are not service pack related. Before you go logging a job with Microsoft I would take a look at:
1. Your SQL Server Error logs. Make sure there's no problems in there
2. Check your Windows event logs and make sure there's no problems in there too
3. Check you're physical server and make sure there's no errors. (Eg. Failed RAID?)
4. Run perfmon and check for bottlenecks. A good place to start is your basic server vitals (Pages/Sec, CPU, Disk IOs)
At least if you do the four steps above you can rule out other server problems.