Autopromote to Queen is a must, as suggested. Qgil's description of making a move is probably the best way on a tablet. It's way too slow for 3 min or faster chess, but as I said, I don't think tablets are really usable for fast chess, which I define as 3 min and faster.

It's nice to have a choice of chessboard colors and styles. I will never use a board unless it looks pretty standard, and telling the light colored pieces from the dark colored pieces is important Of course, one huge advantage of Internet play is that you and your opponent can be looking at completely different chess sets.

Computer chess is really not fun unless you happen to have a sophisticated program that sacs like Tal; that would be interesting. Computer chess IS useful for analyzing games you are watching online, to answer the age-old question: Who's winning?

The ability to set up positions is essential. Say you are looking at a positions with just pawns, kings and knights; you don't want to have to play from the beginning to get there.

Couldn't you just have a completely separate window for chatting? I haven't read some of the comments closely. (Trivia: on ICC, channel 97 is occupied by many political fanatics who mostly talk politics and rarely play chess!) Disclosure: I worked for ICC for a few years and was a member for many.

As qgil mentions, seeing a player's rating is important. I primarily use a Linux program called Jin for playing chess, and I often have a problem in that I can't see the rating of players who have very long names, because the rating displays on the same line.

For faster games, it would sure be handy to have a sound warning to remind the player that only a user-defined interval of time is left for him to make his moves. Example: a three-minute warning, for longer games.