The banning IP addy isnt as easy as it seems.
I moderate on 2 or 3 sites and if I look at my IP address (which changes every few days) the posts with different IP numbers are still all thingied to me (sorry couldnt think of word I needed) which seems like its an easy way to ban a user.
But there could be more than one person using the same lappy/pc or with wireless there could be more than one person using the ISP. At our house alone me, my lad and my fella all have accounts on here, so if I caused problems and the IP addy was banned then everyone else who posts from our house would be banned.
Also there is one ISP that seems to have limited IP addies, I know that at least 4 people on one site where I was a moderator all showed up as using the same IP addresses(even though like mine they changed every so often) This would have looked like the same person but I had met some of the people so know for a fact that they were all different people using the same ISP. The people were as far apart as scotland and southern england yet still showed up in the 'users posting from this IP address bit'