Hi
I run a multi-user blog though we're all in the same “group”. We use it as a diary, each one of us posts an entry every day. I don't know if this would be too complicated (for me it would surely be) but a plugin which allowed the users to rate each day (Great Day/Nice Day/etc… - maybe 1-5 would be better, it was just a better way of demonstrating) and, now's the worst part, and was able to create statistical graphs from the rating average. Ok maybe this isn't such a good idea for everyone else but for this kind of diary I think it would be great. Plus to create the statistics it would probably have to run some process, maybe integration with BatcH for users withouh cron access?
Check out http://www.dailydiary.com (the new home of the original DailyRating)!