I never get them as I am constantly logged in on my PC.
My suggestions would be to use Firefox as it's the most secure browser out there, keep a good anti virus and anti-spy ware software.
If you get anything they'll catch it. I don't think they're malicious though, they're on a lot of sites. They just list googles searches for tags on this forum. Not necessarily the sites themselves, like alla and somepage do. Those are the ones that cause the damage. But I would play it safe, I've seen a lot of those banners and I'm still virus and keylogger free.
I'll take a look at turning them off though, eliminate the risk entirely.