Thanks for the responses.

I've calibrated it in the DS menu but unfortunately it doesn't help.

I had a look around before posting and found a post about it, but it didn't seem to be thought of as much of a problem there so I get the feeling mine might be worse than others.

Is it a general problem that the touchpad becomes less accurate the further away you use it from the centre? It is perfect in the middle for me, but there's so much of a difference around the edges that it's difficult to use for selecting actions, etc. I'd have thought that would have a simple fix, ...