I have a Bike Friday "Pocket Rocket" (the unfortunate shared namesake for their road bike model that also refers to a popular model of vibrator) and love it. It's my "fast" bike for real. I keep up with all the venture capitalists riding carbon fiber on local weekend routes. They're not cheap (all models except the aforementioned Tikit are custom built in Eugene, OR), but they also don't feel like they're cheap. I've tried out cheaper models that are designed specifically for quick-folding or multi-modal commuting and they felt...cheap. Very useful, but not something I'd want to ride 70 miles on.
Something others have not yet mentioned is that there is some getting used to the way bikes with smaller wheels handle. In general, the handing is "quicker," which some folks might call "squirrelly" before growing accustomed to it. Once you get used to it, though, the handling is great. I'm generally a chicken on descents, but I've noticed I'll do the same runs quicker/more confidently on my folder.
I take it with me when I fly on business trips and also like riding 40-50 miles to a good state park to meet my girlfriend for some hiking. After some nature-walking and a picnic lunch, I just fold it up and stick it in the trunk of her compact car. I haven't toured with it yet, but foresee using it for shorter trips overseas.