I'm seeing 705 and 711 in HD right now--alas, no soccer broadcasts from Mexico in HD, though.
Comcast did tell me that very soon they're going to move all the 900 number HD channels to the 700 numbers and move all the music channels to the 900 numbers--a setup similar to what they've done in the Bay Area.
My guess is that once the transition is complete, Digital Preferred customers will get circa this these HD channels:
Discovery HD Theater
Fox News Channel
Fox Business Channel
The Movie Channel (TMC)
Comcast has not said if they're going to require an SDV adapter box if you own a TiVo Series 3 HD or TiVo Premirere DVR box, though.