I would like to see a cut down client that esentially did the 'won stuff', that could be launched quickly or integrated into the game shell and didn't have a gui or any of the auto update stuff so 3rd party browsers like ASE could fire up steam games instantly. Ok it wouldn't have buddy lists but it would make alot of people feel better.
When we wanted to we could load the main program and manage installed games, check for updates buy new products etc.. that would be a sensible compromise and also reduce the number of running processes if world + dog decides to all launch their own steams.