The other day a new comment system appeared on Valleywag and probably yesterday, a "preview" link went on Kotaku posts for it. As I said in reply to Greg's post on product.kinja, where he says it's going to other blogs, I believe his timestamp may be off and this is all new.
Well, anyway... maybe it's my browser, but I'm only seeing a "preview" link on Kotaku, not the other blogs Greg lists as participating in this beta (over the past month?). You can turn the comment beta on for any blog, those he lists or any of the others (including Crosstalk) by appending ?webchats behind the URL. It will then stay on for that blog until you turn it off (or maybe restart your browser). To turn it off, you put ?webchats=off behind any URL.
ETA: I'll keep a check on Greg's post, the one where he's seeking feedback, over the weekend. Anything that I consider constructive, whether or not I agree, I'll ungray.