In beta at the moment - It's basically tetrisfriends.com with actual multiplayer. http://www.tetrisfriends.com/games/Live/game.php Discuss. Note: I think that link will only work after you've signed up for it through tetrisfriends.com
People should start getting into this. It's looking to be very similar to Tetris DS wifi for the PC, with a few alterations and the addition of things like custom DAS.
IRS and IHS are promised. Custom in a way in which I don't know because it's still in Beta and the options screen isn't working yet, but it has been promised.
That's actually real interesting they are going to put in initial rotate, but I don't see how you can use it other than during line clear delays.
It's useful at high speeds for sure, even if it only comes up with line clears. The main thing for me is that I expect it to happen, so when it doesn't I make misdrops.
Funny story: Tetris Friends used to have IRS/IHS and I used it all the damn time in Ultra. Then, one day, TTC said they had to go for some undisclosed reason. Apparently it gets to come back now.