nabla's post seems sarcastic to me, and he is true. What's the worth of pre-manufactured words of thank, that might be sent out automatically to every purchaser of a membership?

The best thank is to maintain the site well. And there I see some possible improvements. It annoys me that bugs in the game implementations, the most important thing of a game playing site, are often not fixed as soon as possible. For example the return-bug in espionage, see here or here .
Fixing bugs in the games should have priority over all other things. It is not a shame to make bugs, every programmer does it. But it is a shame to put them at the far end of the todo-list, where they may remain for years, as in the example.

And the rules description should be complete and conform with the game implementation, so that the players know what they are playing. E.g. the espionage rules should explicitely say that the spying of pieces takes place after every single movement of a piece, but not after the whole turn when captured pieces are already removed (I would prefer, though, to change the implementation to the latter, but I can't say how big the effort would be). This was discussed and proposed already on the espionage board.

Another thing I'd wish is that the game notation gives always a complete description of the game, containing not only the exact moves made by the players but also the random decisions.
For example Dice Poker: currently it contains only the dice after the last roll, but not the re-roll decisions of the player and the dice before the re-rolls.