I started wearing Invisalign in late January 2008 and was told I would need 36 weeks of treatment. I initially went in because I had gaps between my top front teeth on the right side that bothered me and also because I wanted to straighten my teeth overall since I've noticed people I'm close to who are aging and their teeth are becoming more and more crooked. Since I'm in my 30's, I did not want to go through wearing metal braces; I'd already had them as a child. I was getting married in October, so I was excited that my teeth would be finished by then. However, it is now almost April of 2009 and I still have 10 more weeks left to go (supposedly).
Yes, I saw changes in my teeth and apparently needed straightening that I didn't even know about since it wasn't obvious, but the Invisalign did NOTHING for the teeth I was concerned about during the entire treatment. When I completed it, I let my dentist know I wasn't happy with the results, so she ordered a "refinement". It took 3 weeks after the fittings to get the refinement and I went through 8 more weeks of treatment; the gaps STILL weren't fixed. I went in for fittings AGAIN and my dentist ordered a second "refinement", which didn't arrive for 6 weeks after the fitting. I'm now trying to finish up with the second refinement and it looks like the gaps are FINALLY closing.
Considering the fact that Invisalign is so costly (more than twice the price of conventional braces), I've been very disappointed with the results and lack of service. I was also disconcerted by the fact that the Invisalign website doesn't even have contact information (outside of a mailing address) so that you can communicate to someone there that you are disappointed in the progress of your treatment.
If I had to do it all over again, I think I would just go with conventional braces, perhaps the clear ones or the ones placed behind your teeth if possible (for the purposes of cost as well as expediency). Also note that it can be VERY easy to throw away your aligners by accident. This happened to me once and it was an expensive lesson to learn. Don't ever wrap them up in a napkin!