If I recall right most IPs are not static IPs are they?
For like AOL and cable modems, don't they cycle your IP?
I could be completely wrong, but I only access my site from two locations, yet I have a good 30 different IPs listed.
Also, if I recall right, the issue with banning IPs is that you can inadverently block more then one user.
Hopefully someone that knows more about IPs will reply and verify or correct me as I'm very curious myself