I'm interested too as I have exactly the same problem on the 950. In fact I came on here just now to ask exactly the same question and I'm surprised nobody else has mentioned it.
On the 930 it was fantastic, I mentioned in several posts how impressed I was with it's uncanny accuracy. I actually used the 930 for a day again yesterday to make sure it wasn't me imagining it was better than it actually was, but you could almost use it without looking at the screen and certainly didn't need to spend much time correcting anything.
I don't know what they changed but it's now one of the worst features of the phone, as you say, almost unusable. I had hoped it would 'learn' and get better with time but no change, if anything it seems to be getting worse so if anybody knows of a fix I would be very interested as I've now gone back to my laptop to type even short messages.