I bought a Dahon Vigor P9 a year ago and thought it was about time for a review. It's light weight (for a folding bike) at 25 lbs and has 9 gears with a good range. At $800 it is priced halfway between a cheap Camping World bike and a high end Bike Friday. Bike Friday does offer an $850 model, but it is considered a travel bike as opposed to a commuter bike; the difference being a travel bike folds to smaller dimensions but takes longer to fold and may require tools, whereas a commuter takes seconds to fold. Even though my primary use is for travel, the commuter was a better option for me because i can fold it quickly, slip it in bag and store it in my hotel room (or TT).
I bought a cheap Samsonite roller suitcase at Ross which holds the bike securely and doesn't incur any additional airline charges.
Riding the bike is a blast. The small wheels feel a little squirrely at first, but are very agile once you get used to them. The frame is rigid enough to climb steep hills yet quite comfortable. It has an adjustable handle post, so you can switch from a bent over aero position to an upright cruiser position with just one quick release (an additional bonus i hadn't thought of before buying this bike).
For anyone in the market for a high quality folding bike but doesn't want to spend thousands, this is an excellent choice. 2 other bikes i really liked were the Tern Verge P9 and the Novaro flyby (@ REI). If you have any questions don't hesitate to ask...2 things I love talking about are bikes and campers!
John