Pay attention to what you're running in the background. If you want to assess Bounce itself, run it after a reboot (after the device has settled down) and in offline mode. Noticeable stuttering is perfectly normal when you have half a dozen tasks doing their things in the background (or plainly taking up memory).

Also keep in mind the N900 is pushing around 2.5x more pixels than, say, the iPhone. It would probably help quite a bit if there was an option to halve resolution.