I started in March 2008 and I have 13 trays (both top and bottom), a total of 26 weeks. I am on tray set # 9.
I am completely satisfied with everything about Invisalign. Granted, the pressure (not pain) is annoying when I first switch trays every two weeks. But after the 6th set, I stopped taking advil since it's tolerable pressure.
My dentist is awesome and has been upfront with me from day one. I had read the reviews on here and learned about the attachments, possibility of rough edges on the trays, pain, etc. I asked him about all of these possible side-effects and he was completely honest, explained everything and also said every situation is different.
Nothing was going to make me get traditional metal braces. I am 28, with a spacing problem. I have/had a relatively large gap in my 2 front teeth and slight spacing on the bottom, which was hardly noticeable. I have 7 attachments, and after the first week, I hardly noticed them.
If you are a good candidate for Invisalign but are concerned about the bad things - know that if you floss, brush, rinse (listerine Tartar Control is GREAT), keep the trays in for more than 22-23 hours per day, use the "retainer case" that is provided to hold your trays while they are not in your mouth - you will only have good luck. I also use the Listerine Tartar Control to soak, and then sonicare my trays about every other day to keep them clean.