[PhilD]

You can play a multiplayer game with the demo (in fact, my first MP game started as a demo game, though we all moved to the full Version rather quickly).

The possible problem is, the demo isn't (AFAIK) patched to the same level as the full game, so that if you play in MP using the demo, each player has to use the same Version - they may use the full game (and if so, will get more nation/research options), but everybody has to use the same Version (I think the demo Version is 2.08).

I don't know what were the main bugs that were corrected in 2.11, but I know there's a feature I'd sorely miss if I had to revert to 2.08: the fast battle replays...