[cherdano]

If I remember rightly, this has been suggested deep down in some other thread, but I think this would help so much reducing the Lobby noise, that it is worth mentioning again:
I think the default recipient of chat should be the sender of the last private message received (same as now Ctrl-R). Chatting to the lobby should require an active decision (such as Ctrl-L).

If you inadvertently send chat to a single recipient instead of the lobby, you annoy one person; the other way round, 5000 (well, soonish 10000 ).

I think more than half of the current Lobby noise are messages intended to be private (and sometimes the content can be much more embarassing than "I thought you had 4 spades, not 3"...).