There are a surprising number of users on SO who have 0% accept rates. Just today I saw a user who has asked 53 questions and not marked a single one answered! This seems like a huge problem to me, since the system relies on the people asking questions to at least spend a moment or two marking the best answer with a checkbox, which not only improves the quality of the underlying data, but also gives back some love to the answerer for the time they spent helping.
I would like to see a system where users with low accept rates have their questions approved by a "moderator" (i.e. 2000+ rep user). The trigger point for this wouldn't have to be very high, since not all questions have answered, but some sort of criteria should be in place so people asking 53 questions are basically forced into doing their duty.
This would probably be extended to new users as well (with maybe a slightly weaker trigger -- perhaps only after asking N questions), to prevent those checkmark-adverse users from just creating new accounts.
In other words, the desired behaviour (marking questions as answered) is encouraged as it removes the trigger, where undesired behaviour (creating new accounts) would be discouraged as those accounts would also be under the same system.
Alternatively, a simple delay (e.g. inversely proportional to the accept rate for accept rates < 50%), could be used to add time before a question gets posted.