I've been using Symantec Anti Virus Corporate Edition at work for years without a problem..... that I know of. The management console is entirely useless, but the client pieces do their jobs nicely with no noticable system impact.

If you're looking for home user AV, then this might not help you. Though, apparently, Symantec AV 10 also has good anti-spyware. I haven't installed this yet to test, but in my opinion, spyware protection is hundreds of times more valuable than anti virus in today's environment. Maybe they're one and the same.