Codeforces has a large competitive programming community, so I think it would be very interesting if it held rated OI style contests in addition to the regular contests (like div1, div2, ...) and each account had two ratings. One for normal contests, and one for oi style contests. what do you think about it?

What is the most interesting problem you've seen in Codeforces? Send it in the comments. (If you send the link, write its name next to it).