I use Panda Platinum internet security, and yes it does slow down performance a little, but it doesn't use nearly as much CPU as Norton. My PC starts up faster, and works faster than before. Shuts down slower, but so what, It shut down eventualy if I press shut down, no need to watch over it.
I do a full scan when I have some idle time, maybe once a week. I also use the built in firewall.
I also have Spywareblaster and MS Antispywareblaster enabled at all times when connected to the internet, + a scheduled MSAntispyware scan every day.
Ad-aware SE Scan if I suspect something has gotten through my other defences. I also use CCleaner after scans. Just incase.
The one poster that said P2P was safe when only downloading movies and music is SO WRONG. I'm a businesschoolstudent, so I don't have the resources to go out and buy or rent movies, music etc. He should go check out the Gnutella forums for treads about Malware and then come back and apologise for lying. It has almost become an art to manege getting what you want with P2P. I manage, but it's sad to think about all the newbies falling into traps.
I use PeerGuardian2 as extra protection when using P2P apps, pretty effective in blocking known malicious IP's. Remember to update regularly. Link below
PeerGuardian2
I use Registry Mechanic for optimization, but only scan and clean, not the System Optimize, because I find it causes more bad then good (unstable)
and thats it I think