This is a bit concerning both me and my brother play poker on a number of sites we have never played at the same table or tournament but have transferred money to each other and handed the other one straight cash, (eg he would transfer me $50 and i would give him $50 in cash or vice versa) its convenient and a faster way to cash out and see money in your account.
I also have a friend in my area and when one of us is short eg does not have much money on them we usually say ok transfer me $X and I will give you in cash. that is not abnormal as we usually like to keep as much money in the poker accounts as possible so we can move up and etc. its usually only at the point of been desperate that cash outs occur.
albeit this is usually only small amounts vast majority of the time its $50 it has been a little more occasionally.
this has been done on both pokerstars
and full tilt only. We have never had any problems from any of the sites for doing this. I don't know why we would?