If some one banned me because my ip didnt match the last time I logged on you better believe I would raise hell. I'm on dial up and I have at least 6 differen IP's 3 of those starting with different numbers. Like 201.**.***.*** or 46.***.***.*** If some one went on this information and banned my account I would be raising hell every place I could think of and I'm sure Unixmad and Stefan wouldnt appreciate something like that. ;x So in short this is a very bad idea to ban some one because IP's arnt all the same. Although if some one logs on and reports a hacker it would be very handy because he could talk with the staff and let them know which ip wasnt his.
It's all in usage.