As reported by Damir and Tim Sneath, we have released a vector-based illustration tool that we acquired last year from Creature House called Expression 3. Downloads are available for both Windows and Mac. There’s also a quick feature tour. From some of the comments I’ve read on other blogs (and in the Expression forum), this sounds like a pretty capable tool. Enjoy!
To give you an idea of its sophistication, here's a screen shot of one of the sample files: