I bought my MBP in September (five months ago) and this problem appeared about two months ago. It progressively got worse, until I was unable to draw in Photoshop, drag windows around, or resize stuff. What a pain. And pretty disappointing for a brand-spankin-new Apple laptop.
After the quarter ended and I could be without it for a while, I had a genius look at my laptop. As you might have guessed, the entire trackpad assembly was to be replaced. It was a $135 affair, but covered by warranty.
The new trackpad works great (three days post repair now), and I really love the laptop.