You cannot play on the same table on the same IP address, other than that im sure it happens, BUT they do have pretty good collusion software to detect this, (aka if it happens often or if I am RR with weak hands and you have great hands just to get the pot big and then fold to you.)
IF they catch you doing this they will ban you for life and take all the money in your acct.
IMO- ppl would only do this at super high $$ tables anyway, why would you waste your time cheating at low tables for $20 pots when you could be winning $1000 pots