Having reflashed and reinstalled everything step-by-step, I'm pretty convinced that there's some conflict between BlueMaemo and version 49 of Power Kernel - the one currently in Extras-Testing. Without that, pointer movement is as responsive as can be.

I also got the hardware keyboard fixkbdfocus trick to work, though I will try to find out how to make a shortcut icon that launches it with the command. It's pretty tedious to do every time.

The one remaining problem with BlueMaemo then is that the hardware keyboard function (blue) keys don't map to the correct characters. They're in a completely different arrangement! (The one from 810 maybe?) My workaround for this is to open the Bluemaemo soft keyboard on its special character page and use those. Works well enough I suppose, but a bit irritating. Did anyone ever find a fix for that?