Jason Snell from Macworld has the best review in my opinion of the HP Touchpad. I read all of the reviews from Ars, WSJ, NYTimes, and around. Snell is the only one to mention how the Touchpad interfaces with the Mac.
Looks like a promising product. They did lure/steal Apple engineers to Palm, which is now HP, to design the WebOS. Apple could take some design ideas from them.. like the way they end apps.
Read the full review here