Is Anti-virus/security Really Important On Droid Phone?

I recently purchased a Motorola Milestone, and I absolutely love this phone. But I’ve seen a few security apps in the market (an anti-virus one and Lookout Mobile Security are the one’s I recall). Reviews of these apps say they’re good, but that they also consume an insane amount of battery life. So, what I’m wondering is, is having something like this really important? I haven’t and don’t plan to install any third-party apps, and I use the same basic common sense while browsing as I do on my computer. (Even more so on the phone since I do have an anti-virus program on my laptop, which probably give too much of a sense of safety).
I think I heard somewhere that when you connect a device like this to your computer, your anti-virus programs scans it to- and I connect my phone to my laptop quite often. Info on that: I use Norton 360.
While we’re here, any free apps that you would recommend?