Only one problem with banning using that method... usually leads to more than one person being banned and that tends to piss people off... especially if they haven't commited a bannable offence. Dynamic IPs are really difficult to nail down, so you end up having to ban a whole range of addresses to ban just one guy. I suppose if every AOL user that connects to your server is cheating, then that would be acceptable, but I wouldn't think so.
As for them being the largest, yes that is true... but that doesn't mean that these cheaters are using AOL. Usually anyone that's serious about gaming online will avoid them like the plague. Some of them may even be on broadband connections (dynamic IPs are available from some ISPs.. and I wouldn't think AOL would be one of them)... a dynamic IP doesn't necessarily mean they're dialing up with AOL. What it boils down to is that in order to ban one specific person, you will have to ban a whole range of IPs... hope you don't get any hate mail over it.. heh.
<font color=red> If you design software that is fool-proof, only a fool will want to use it. </font color=red>