Usability 
Mobility.mobi - I can't believe I didn't see this site before. Mobility.mobi is a nine month old online forum dedicated to discussing the mobile web and especially the .mobi top level domain (TLD). It's very active with over 7000 and threads and 46,000 posts. Lot's of discussions of new mobile sites, industry news, SEO, domaineering and buying selling and trading .mobi domains. There are also active sub-forums for mobile web development questions, discussing mobile publishing platforms, hosting and legal issues like domain name disputes.
Mobility.mobi uses browser detection to display either the full PC version of the vBulletin based forum or a mobile one using a great mobile template developed in-house by mobility.mobi. There doesn't seem to be a way to force the mobile version if browser detection fails although I wasn't able to make it fail with any of the dozen or so mobile user agents I tried.
Mobility.mobi's mobile front page mobile scores a perfect 5 out of 5 on the Ready.mobi test. The index pages listing the posts in each forum and the post pages themselves can get quite large however, well over the10KB of markup and 20KB overall limits generally recommended for "one-size fits all" mobile sites. If this causes out of memory errors on your phone, if you're a registered user you can change the number of posts per page from the default of 25 to five on the Options Page which should help a bit. You can only change settings from the PC version though.
Except for options, the mobile version offers almost all of the functionality of the PC site including posting, private messaging and registering for the site. It's not necessary to register to view the site except for a few members only sub-forums. You have to register to post, of course.
It's really inspiring to see Mobility.mobi doing so well. Anyone who has any doubts about the mobile web's vitality should spend a little time poking around. There's a friendly, cooperative feel to mobility.mobi with developers and publishers helping each other out without any cattiness and flame wars so common to online forums.