To some of the questions:
1. Message of the day could be interesting, I imagine that would be something server admins would set? Sounds like a good mantis suggestion.
2. The steam overlay definitely works with all arcen titles, but we don't do any particular integration with steam beyond achievements. So you can't invite your friends to a game, for instance. But you can chat with them like normal and say what server you both want to hop on.
3. The screenshots that Valve uses are all ones that we submit to them; in the case of which one gets used as the background, I'm not yet sure. That was a new feature since we last had a game launch with them, and they chose one of our screenshots themselves. But I presume that normally they let the developer choose a specific shot.
4. We're always wanting great action shots to use for our screenshots in general -- always a challenging thing, and so we can always use help!