One thing that bothers me about the game is the invite system. If you're in the middle of a game and a friend invites you to play, you don't have a way to send him/her an in game "e-mail" if you will, that you will or will not be able to play. All you get is accept or decline.
Most of the time, if you're in a tourney or with other people playing, your not going to quit. In a way, it seems kinda' rude to just decline and not give a reason why. If you want to except the invite, you can easily chat with the party your with and tell them you're leaving to play with a friend. Also, it'd be really nice to be able to send such an email, if you were trying to start a group with some friends, it'd be cool to ask them if they were in the middle of a game as well.
One game that I used to play (a console game) called Phantasy Star Online, had this type of a system. You could be in the middle of playing the game and get an e-mail and you could answer it at your leisure. Whether or not this idea makes it to the game, I feel that you guys have done a great job so far. Please keep up the good work.