I've had one in mind for over a year now and xF has inspired me to sell my vB license, buy the domain for the new project, and to enjoy "playing" with something new. Everyone likes new toys, right?
Mines going to be a forum for geeks - I'm a self confessed one myself anyway, but fancied chatting with like-minded people and needed something to distract me from the hard work that has been converting my main forums at CycleChat.
I'm holding out for stable xF before putting anything "live" but it's nice to have something different to play with. Especially something that's compulsive to use through its simplicity.
How about you?