Product review (5 stars): Amazing, great product that can clean ducts with multiple turns/joins.
This was just an incredible product, and it pays for itself in one use.  It was slightly horrifying and satisfying at the same time when all the lint came out.  Basically the way it works is this...

1. Instead of running the duct to your dryer, you run it to your vacuum cleaner.
2. You hook up this attachment to your drill and thread it into your duct from the outside of your house.
3. Spin it up as you clean out your duct and your vacuum cleaner will suck up all that lint which was previously hanging out in your duct.

Tips:
1. The vacuum cleaner attachment won't create a perfect seal, so use some tape to get a good seal between your vacuum cleaner and the attachment.
2. Give the drill some gas!  Don't try to start the spinning action very slowly or you'll just get the extension twisted.  You need to gun it to overcome the initial friction created by the cleaning head.
3. Don't forget to tape the connections, it's possible that you lose one in your ducting.
4. Only spin clockwise!