AVG free, I'm running 8. Has some slightly annoying nags but hey, it was free.
I back that up with threatfire because I've been known to open some rather nasty stuff in the past accidentally.
I love it when a trojan kicks into gear and gets slammed to the mat by threatfire asking me if I want to allow this process.
The 2 together make a very good low impact combo.
Yup, threatfire can be a real solid last defense, it will catch a suprising amount of stuff that even NOD or bitdefender miss. Now it will also annoy the beshesus out of you occasionally for no good reason (at higher settings) but its a very good "extra layer", especially with any of the basic (read free) AV programs. As someone else noted its got an odd usage footprint. 98% of the time its very low impact but it can balloon badly on occasion...
