I ride DART enough that I've been thinking about (and doing some digging into) folding bikes -- lower-end ones, admittedly, but folding nonetheless. Whenever I do take DART, the furthest I have to go to or from the station is about 2 miles. Additionally, part of my DART riding is on the smaller "flex" buses, and I also want to be able to put the bike in the back of Terrie's Prius -- so for all the above, a folder seemed like a practical option. Mark Colletti purchased one back in the summer, but I forget the brand name.
After a bit of test riding, it came down between a used Breezer IC3 with 16" wheels, and a KHS "Mocha" with 20" wheels, both under $400. I wound up purchasing the KHS, because of somewhat more substantial fold interlocks, adjustable height handlebar, 7 speeds vs. 3, and the 20" wheels. It folds and unfolds in about 30 seconds, which is reasonable. It's certainly DIFFERENT riding a "DF" style bike again, especially with 20" wheels -- but I won't be using it for long distance or club rides. Here is a series of pics: