As far as i can see there are no problems with Lion or Mountain Lion. Due to some right-related things you perhaps have to delete in the preferences the com.stone-stuff (exept the license) for some things like individual patterns etc. are stored in the library and may not be accessible.
What definitely not working anymore is the image-well / gif-export due the program that makes the gif is ppc and so not supported neither by lion or mountain lion.
(I would love to see a statement from Andrew whats up with Stone. No updates for years, just the Vidiator in the App-Store (Why that? Create wasn´t worth?). PStill would definitely need an Update to support the lasted PDF-version.
I begun looking for other drawing-software in case Create reaches its end. I like iDraw (if it matures a while), Intaglio (a reminiscence to MacDraw) and EazyDraw (Mighty and powerfull, first choice for me if the programmers finally learn that good software is not just a bundle of features but an easy to use interface) But all somehow lack the fun of using Create or its ease of use.)