LOTRO started offering a large number of incentives very early after their launch, and they seem to be doing fine. The $50 entry barrier is a bit steep, and anything that brings it down can only help the game.

The real question is whether they're policing the system so to catch people whose invitees "coincidentally" all turn out to be gold sellers - pretty much every game I've played suffered a massive increase in spam after starting a free trial program.