I played some when they first came out.
$.75 from each player is taken from your chipstack and put in front of you.
If someone wins a hand with 7/2, including bluffs or any non-showdown hand. all of those $.75's go to him.
If you leave the table, you take that $.75 that is sitting in front of you back.
I started playing them when they first came out and they were really wild/aggressive. They've calmed down considerably since then (keep in mind this is based on a small sample size).
I still think they attract looser players, but people have learned that not every big bet means he's bluffing
with 7/2 and playing a big pot with your 7/2 bluff is not always advisable.