Choosing to relay should not default to being an exit
In the 'Sharing' tab on Vidalia, there are three choices: -Run as a client only -Relay traffic for the Tor network -Help censored users reach the Tor network
The second option creates an exit node, not just a middleman relay. A user has to manually go to the 'Exit Policies' sub-tab and un-check all the boxes if they only want to be a middleman.
Running a non-exit relay is very easy, requires almost no work, and is unlikely to create trouble for the user. Running an exit takes a much more considerable amount of work, and can make life very difficult if the user isn't expecting it. Since only prepared or experienced users should consider being exits, it makes more sense to make non-exit relays Vidalia's default.
To further reinforce this point, perhaps setting up an exit should be accompanied by a more extensive disclaimer, referencing /Tips for Running an Exit Node with Minimal Harassment/, or a similar resource. I suspect that many folks avoid running relays because they use these default options, receive a nasty letter from their ISP, and don't realize that they can run a non-exit relay instead. Another choice to reduce the pain (and therefore attrition rate) of exits might be to offer the "reduced exit policy' as an option out of the box, rather than forcing the user to find and implement those resources on their own.