The battery on my MacBook was bulging which was putting pressure on the trackpad, causing it to "stick." It eventually got so bad that it was impossible to use. Very annoying.
Easy fix--just removed the old battery, and slipped in the new. Took less than a minute, start to finish.
This was an incredibly easy fix. My MacBook is getting a little old ('08 model) but it still serves my purposes so it was worth the cost of a new battery. Couldn't find a better price anywhere, and the repair guides were clear and helpful. I only wish I had done this sooner!