I got invisalign on a whim last year, when my dentist was having a special deal. I do admit, it was a very good price comparatively to other dentists. I have fairly straight teeth, but they bow toward each other and inward (like Lindsay Lohan's teeth) and I also had an overbite where you could not really see my lower teeth.
The dentist did not explain anything about the procedure, so some things were a surprise to me. They told me I needed "attachments" on my teeth in order to keep the trays in. These attachments are little white nubs that are permanantly glued on your teeth, for the duration of the process. This means that, depending on how many attachments you need (I needed 6) people could potentially notice them on your teeth when you do not have the trays in place. This kind of negates the purported benefit of invisalign, since I looked like a weird vampire with the attachments on my canines. I basically had to wear trays all of the time.
I also did not like all of the times I had to go into the office. I had 14 sets of trays, and they would only give me a few trays at a time. I was in there at least every month, just for them to ask me how I was doing then give me more trays.
So after all of this, I have been wearing my last trays as a retainer because I am going BACK IN for a "refinement". My teeth are still inward and the front teeth are not completely straight. I figure I may as well go ahead and do another round, since I paid to have straight teeth. I will update after Round Two is over.