The whole thing seems pretty creepy, but I think it was made creepier by the official introduction of the guy. Like they said, the forums really are open for anyone to create an account, so GEICO could have easily just had the guy create an account and name it what it's named now without having been so official and creating an uproar. I get the sense it won't be too intrusive, but I agree it'd be weird if I was browsing a forum and suddenly someone's username just had fat GEICO plastered on it.
I'm just waiting for their off-topic forum to start a GEICO-bashing thread. Sounds like nothing could go wrong.