Serenity Caldwell does a typically excellent and thorough review of the new pressure sensitive iOS stylus from Adonit. She likes it a lot but the app support is still not perfect:
The result is that while I love working with the Jot Touch, I’m less thrilled about the way Jot Ready apps are integrating the Adonit SDK. Some apps implement only opacity—which I find nigh-useless unless I’m using a paintbrush or airbrush tool—and leave out brush sizing. Others have no way to customize or calibrate brush strokes, a deal-killer for artists who, for example, use more pressure in particular situations and would like to be able to alter the brush accordingly.
I like my Adonit stylus a lot. I'm sure to like my new Adonit touch more.
I think a new SDK is a hard thing to integrate, but just as I expect TextExpander integration with my writing apps, I think I will come to expect Adonit Touch integration with sketching apps. I'm hopeful for that future.