Hi everyone,
I had this exact problem and used this thread as a guide and actually got mine fixed so I wanted to share my experience.
I have a 2011 late model MBP. I bought it in February 2011 and it was about 9 months old in November and I didn't have any extended waranty. One day my trackpad just starrted going nuts (click on it's own, i couldn't move it right, would highlight stuff) just not ususable.
So after reading around I took into the Apple Store. Right away the guy said "yeah you have to replace your trackpad" like it was a common problem. He took my information and i saw that the repair and cost would be $90. It took 3-7 days to fix (5 actually) and when i got to the store they just gave me back the laptop all fixed and the bill was $0.
It still said $90 on the form with amount due $0, i guess to keep track of how much Apple is losing in these repairs. They checked for water damage (I had none) and they noticed i had a small dent on the case (backside, no where near the trackpad).
I hope that helps you in the future. If you are having a simulair experience I would say take it in, worst case scenario it seems, is that you would have to pay $90.
Good luck out there!