That said, there are drawbacks to the Playbook that are hard to ignore and make it hard to recommend as a development target from the viewpoint of a "webkit developer" (oddball term, but there you have it.. :) ).
They feel quite a bit more sluggish than even the iPad1, which is fairly old hardware now. It would be encouraging if at least one non-Apple Webkit hardware+OS implementation out there actually managed to do CSS3 animations even half as smooth as the iPad2. I'm optimistic this is going to happen, but I don't think the Playbook has it right now. One thing I've liked about the Playbook and WebKit implementation is that we're mostly seeing what we interpret as "correct" behavior (aside from some Touch events interpretation, but we just received some help with RIM on that with the touch-mode setting). In comparison, the Samsung Galaxy Tab exhibits crazy smearing and other rendering errors when performing -webkit-transform. Our reference for correctness is Mobile Safari, though it has quite a few fun rendering bugs as well (iOS 5 actually introduced a couple new ones).
I'm not trying to be funny, but one thing that seriously inhibits productive web development on the Playbook is its power button and battery characteristics. Sometimes we literally cannot figure out how to get our Playbook to turn on -- the power button on these things has to be seen and felt to be believed. Sometimes you'll press the power button and it won't come on, and will suddenly spring to life 7 to 10 minutes later while sitting abandoned on your desk. Weird stuff...