My client has a farm with MOSS 2007. Recently they upgraded to SharePoint Service Pack 2. Since the patch we have noticed that the CPU's on the server spike when users upload files. We are not sure whether the cause is the service pack, the fact that we are using Trend Micro OfficeScan Client 8.0 (not designed for SharePoint), or some other factor. Are there know issues with Service Pack 2 or OfficeScan?
To test if the virus scanner is causing the problem, you could also disable the virus scanner and reproduce the CPU spike behaviour to see if the problem dissapear. If it doesnt, try and use products like Process Explorer from www.sysinternals.com (part of Microsoft now) to see what process is responsible for the CPU spike.
If this really is an anti virus case, you should make sure you set up file exclusion to avoid the virus scanner bogging down performance.
Files like log files and templates etc in the SharePoint root (12 hive) should be excluded from scanning or performance may suffer
I read that especially WSS_adminservice.log can cause CPU spikes.
C:\Documents and Settings\Default User\Local Settings\Temp\WSS_AdminService.log