25
Apr
OK, this is not exactly about a particular open question, but I just thought that maybe you will be interested.
IBM Research’s Ponder This features a problem every month and is open to everyone. Check it out!
http://www.research.ibm.com/ponder/
Usually I am humbled by the questions and those that managed to solve them so quickly. But I will continue to ponder it every month. 
11:52 on April 25th, 2005
Yeah, I tried to “ponder” one of them and got nowhere!