Minor collusion such as 2 friends sharing hole card information does not give a significant advantage in most situations and it is generally an accepted risk by most online poker players. Serious efforts at intelligent collusion were simply not worth the effort in SL poker. For the amount of effort it would have taken and the stakes involved on most VGA poker tables in SL, scam artists could get a higher rate of return on their efforts by running other scams in RL, the internet or SL, like, oh I don't know, opening a "bank" on SL. Now give me my pie for slipping in references to both SL gambling and SL banks in my post! 
Im not the pie giver outer person.
I kinda have to disagree - becuase I have heard from some people I beleive -- that it was done, in games they were involved in.