SP2 has some problems if you are running a 64-bit system. I have it on all three of my systems, and it works perfectly - they are all 32-bit and I don't play games.
It gets along just fine with existing security systems, and it's built in Firewall co-exists nicely. Updates were about 7 in the first two months - but they now seem to have abated pending release of RC2.
For my use and purposes, I can live with RC1.
And, no problems at all with optimization/defrag. I do that frequently using PerfectDisk by Raxco.