Mutiplayer.
All the sounds when people join...when they chat...when they pit...and so on. I know you can turn of the messages but all the join/pit stuff can't be turned of as far as i know.
Sometimes this is really distracting and i'd really enjoy it when it could all be turned off.

Cheers

A popular idea indeed

http://www.lfsforum.net/showthread.php?t=304

I did do a search...that one didn't come up. Thanks for the link.