I got mine in late May 2010, was scheduled to get them off in November 2012, didn't get them off until late March 2013. I wore my rubber bands, and did everything I was told. They were just off by a few months. I was told it would take me 2- 2.5 years ( I also had overcrowding, and got 2 teeth pulled from top and bottom). A lot of people I know keep them on a little longer than estimated.
My twin also got hers on in late May 2010 at the same time as me, and she still has hers on. Her estimate was also 2-3 years ( she also had 4 teeth pulled). So the 3 year mark is coming up, and they are not scheduled to be taken off next month when it will be three years. She will have braces past her initial estimate. It's different for everyone though. Honestly, she didn't wear her rubber bands all the time as she was told. Btw, I didn't notice a change in the beginning either, especially 2 weeks! Give it time.