Thank you very much for your reply. If more instances of running program with the same wallet isn't possible, I think it should be documented.
But OK, so I can other scenario:
I have 2 computers, one at home, one at work. I'm running bitcoin at home, then I shut it down, go to work, start running bitcoin there, with the same wallet. Then shut down, go to home, start bitcoin at home and so on. BUT: I don't synchronize files (~/.bitcoin). So I don't run more instances of the same wallet but I don't synchronize current state.
It's this possible? Will be synchronized sent and received payments or are there other problems? Or rather I should use two different wallets, one at home and one at work?