The way I look at it is this. It's the first phone that would cost more than $200 unsubsidized that I have purchased. I had Lookout on it at the beginning but removed it because everyone said that it was unnecessary. After seeing two stories about malicious apps and that Lookout caught them, not Google, I put it back on. It uses some battery, but it's nothing outrageous. On something like this I'd rather be proactive than reactive.
Maybe it's because my desktop got the AV Security Suite Virus a couple of weeks ago and turned it into a large paperweight, but being vigilant is not necessarily a bad thing. That's just me, not saying anyone has to install it, but I wouldn't fault anyone for doing so either. If I did and their phone got screwed up, I'd feel bad about it.