Here's my favorite HD Dslr site
Philip Bloom - DP, Director, Filmmaker
If you read through it, drill down as there are lots of topics in the short time of the blogs existence, you'll see people are using 5D Mark II and 7D for broadcast TV commericals, Saturday Night Live scenes, Even some scenes from Terminator Salvation were shot with 5D Mark II. Music videos are being shot with 5D Mark II too, ect...
Philip also uses Panasonic GH1 and GF1.
I've never seen him mention, not even once using a Pentax for HD.
Thats goes for Nikon HD Dslrs too. He does use Nikon glass adapted to Canon, as many people do.
You'll notice all the assessories on can buy to dress up the Canon's potential.
That said Canon has a rumoured a dedicated HD Camera that accepts Eos mount glass !
Fall 2010 is a possibility.
Canon and Panasonic both make broadcast cameras for TV so they understand better how to implement the HD spec in comsumer cameras. Sony is dragging their feet as they too make high end broadcast TV cameras. Their hessitency most likely impacts Nikon and Pentax, both buyers of Sony sensors.
That all said, I own no HD Dslr, but its fun technology to read about. I could buy a 5D Mark II and be done with camera aquistion, or a Canon 7D, or a Canon T2i. Canon is pulling away from competition offering this one HD Spec in all three current dslr cameras.
Panasonic GH2 rumors are very appealing also, and its due September 2010.
Drill down at a couple m4/3 & HD sites:
http://43rumors.com/ http://www.eoshd.com/index.php
I know of no site dedicated to Pentax HD Dslrs, anyone got a link ???