Full Specifications etc. are now officially online!
http://www.pentax.jp/japan/imaging/digital/medium/645d/spec.html
(in Japanese)
Update: An English Spec can be found at the DPR:-
http://www.dpreview.com/news/1003/10031002pentax645d.asp#specs
And, the "kit" prime lens is here:-
http://www.pentax.jp/english/news/2010/201007.html
(in English)
Sample photos have not yet been uploaded, though.