Wait for Webroot to go on sale at Best Buy, get a year for like $20. I started using it because I got a year for free, it's definitely the lightest AV I've used, not intrusive or loud at all, and has an excellent detection rate.
I wouldn't pay full price for it, but the sale prices are always really good.
Yes. I've seen PCs with "Buy our antivirus to fix all these problems" fake antiviruses and weird toolbars, with MSE happily sitting there saying nothing is wrong.
To be fair most free AVs will let that stuff through
Yeah, no amount of AV protection will stop someone from downloading 20 toolbars, and I'm not sure how they work but those fake AV programs are really effective if you're unlucky/reckless enough to get one. I let a friend use my computer unsupervised for a few hours and he picked that up, it completely wiped out my AV's definitions library without just disabling the AV entirely so every scan came up clean.
Every time I try to go where I really wanna be it's already where I am, 'cuz I'm already there XBL, PSN, Steam, Origin, BSN, GFAQs, MC: PhilOnDez