While running exit nodes definitely seems undesirable due to the volume of abusive traffic that is likely to go through the exit node, I bet other kinds of relays would be a lot less cumbersome. Obviously a very well-funded attacker will always have the upper hand, and obviously, if you were to always use your own node as the guard node, it would lose some of the properties of Tor, but I bet it wouldn't hurt for more of us to run nodes. I am interested.