I had a similar trouble and I don't exacly how I fix it up. It's weird but it's true.
Let me say what I think that solve the problem (Anyway I'm quite sure It was a...
I don't know nothing anymore!
Yesterday after my reply posted here, I checked my N900 that was charging, running the transmission (a torrent application), It was very very hot and there was a error...
My problems went away just like it cames...
Since yesterday the touchscreen have become more and more responsive and now it's completely normal! Uber weird!
I'dont REALLY know how it's working again
The same thing happened to me! There is a details that occurs to me and Sunny didn't say. When I press the numbers on the screen the phone seems to respond...it shakes and everything!