There's a name for this, "Collusion". I'm sure it says somwhere in the user agreement that you must play only in your own intrest, just like it says on the sign in every poker room.

I would warn your friends that poker sites can and will check folded hands if anybody e-mails them with a complaint. I know of 1 person who is banned from party poker for life for that reason, and the money in their account was forfeited. I won't go into details about how they were caught or how they were doing it because I don't want to educate anyone who still wants to try this.

In a SnG or a limit game collusion can give 2 or more players a very unfair advantage, and would be profitable for them in the short term. In the long term these players would be banned from every poker network out there and have large portions of their bankroll seized at inconvenient times.

Consider the amount of time spent comminicating. Why not use that time to play on more tables? I can't imagine colluding on more than 4 tables at once. Collusion would increase your short term profits but I don't think they would double. You would be better off 8 tabling and playing straight up than 4 tabling and colluding. Unless you don't have the skill to beat the game straight up.

The low limit players can be beat without colluding and would probably have no clue if they were being cheated. The high limit players can spot possible collusion and would have your play investigated so fast it would make your head spin.