I've never used one. I do take some precautions though. I do not do any banking on my phone, I do not download an app unless I read good reports about it either here or one of the other sites I trust.
Android user since my Droid launched( Nov 2009) and don't ever use it. Carry the same attitude as you do with anything electronic you buy..ie,buyer beware. Same goes for task killers will never use them.
Nope. Android operating system is different than windows. Malicious apps cannot spread to other areas of your phone. Also, your phone's default setting is to only allow apps from Android Market to install. Leave that setting the way it is and you'll be just fine. Android Market apps are screened and people give feedback to let you know if the app is garbage or not.
When web surfing, programs cannot install or invade your system.