On a JFK/SFO flight due to flying around thunderstorms the a/c is running low on fuel. The Captain comes on and tells us we are diverting to DEN for fuel. Captain then says "for those of you that have always wanted to go to Denver you now have your wish. For those of you who don't, well you going there anyway." Then we get ready to take off from DEN and Captain tells us that ATC has put us on a 20 minute hold but tells he is not getting his hopes up about being released in 20 minutes and neither should we.