sure its possible, and I havent heard of any mass account bannings from myspace but one never knows.
Better safe then sorry is my motto, but I wont worry about it till you start hearing ppl getting all their accounts canned in one swoop.
I'm sure you could have tons and tons of accounts because kids using proxies at their schools, and more kids at other schools on the same web proxy would all be connecting to MySpace through that one proxies IP, which would be a lot of people. They're able to do that so why not.
It only when you signed up, you have to use different ip,but when you got the login, you are free, buddy~