One thing to remember Antivirus programs are not just ANTI-VIRUS, they are designed to detect any program that has excessive access to the file system and/or memory, or that attempt to modify stock system code, which is one of the reasons ROM Manager gets tagged, it is able to modify your boot partition.
There are malicious apps on the market, and they don't always get caught by Google before they get out, so it does not take a genius or a moron, to get one, it can just happen ....
Antivirus apps are a double edged sword, they can save your ass, or prevent you from doing something you actually want to do , as with most things in life, they should be used in moderation ....
I personally would rather have a AV app that is a little over zealous, than one that ignores a potential threat ...
The biggest annoyance on android right now is Air-push ads , while not malicious they are annoying, even more so when the publisher does not inform you that they are the "ad supporting" part of the app ...
So IF you are app happy, and install tons of apps, an AV app may be a good thing for you ....
Call me paranoid, but I usually don't install an app from a NEW publisher that has not been on the market at least 30 days, I usually check and see what other apps are put out by a publisher as well ... IF you only see ONE or TWO apps by a NEW publisher, then you might think twice, until reviews start flowing in ...