For quite a while now I’ve been working for a startup from Eastern Europe - globalcasting.com.ua
The whole thing work like this: users register, post few pictures, then they can join weekly contest, which is a basic rating-like system (stars); during work days (monday-friday) each user can get votes from any registered user , and this activity creates the “top-15” users, who are then rated by jury (staff members, I believe) and ultimate top-5 winners are being rewarded with real cash. The whole idea is somehow connected to showbiz and photo model biz, in finding new faces etc. - it’s not at all important at developers forum, I think.
I’ve been invited to develop the whole app from scratch - and the only reason I was able to do so is that I had learned Yii pretty well by that time (work started somewhere at the end of Q1 2010). There is a saparate parts of application - frontend and backend (administration, staff members).
As easy as it sounds, it all got a little bit complex over the time (over a short period of time, actually): roles, professions, access control; contests then had to be bi-weekly (well, custom period), we had to create moderation system (for users in general, for those users who attend a contest, for profile comments); commenting system (I quite a few unusual task here too, like copying the whole thread between every party of that thread, excluding some cases - of course); ratings (of few kinds) and much more; search filters with ajax-powered content loading etc. My partner on that project (who joined my one-man-team a few months after launch) also had quite a few interesint tasks (unfortunately I’m not sure if I can post more details about this before checking with client).
I will try to answer some of your questions, though some might take time to check with a client.