I have a similar issue -- a 2008 black 13 inch MacBook that has taken to inserting the cursor wherever it feels like when I hit certain keys, such as "y" or "u". Very annoying and non-productive.
I've carried this laptop all over NYC & the country and the bottom doesn't sit fully flush with a desk anymore, so I fear this is something that time & use has done to my machine, but would love to know what exact cause & remedy is.
Okay, after searching here and elsewhere, I may have come across the problem:
a swollen battery!
Check this thread for battery info...
but apparently over time gas collects ins 4 foil envelopes contained in the battery which then bows out the surface that then impacts the keyboard & trackpad. Right now I have my battery out and not only is my computer sitting flat on the desk again, but the keyboard is functioning well again.
I'll have to think what I'm going to do about replacing the batter.
Hope this helps.
There’s one problem with running your MacBook with the battery removed. MacBooks and MacBook Pros automatically reduce the processor speed by about half when the battery is removed.
You can get a new third party battery fairly cheap on eBay
Or for $129 from Apple http://store.apple.com/us/product/MA566LL/A?mco=MTY3ODQ5OTY