As mentioned in one of the few discussions about this subject, we have made few attempts last year as well earlier this year to develop a mobile skin, but we kept on running into issues with existing solutions available with the particular version of the vBulletin we are running.
I am 100% with you on that one. I've never been a fan of mobile sites for forums specifically. For publisher-centric content-rich sites it might be a better idea, but for a user-generated discussion forum - how much typing can you really do on your little device?
We have a mobile skin for TalkFreelance.com forum, which I've been on perhaps just twice this year.