Here's my bike. I rode it 5 miles to school today, and will be riding another 5 to get home. I'm writing this from my laptop (more later), and I took the train as well as my bike (more on that later too.)
Here is the webpage about my particular bike, although the Dahon brand offers several more really nice ones.
Yes, it folds up. Yes, it unfolds to be a regular, full sized bike. Yes, it works just as well as any other bike. Better than most, actually. It has 8 gears, in an internal gear hub, and I've had it for a bit over a year now, with absolutely no problems with the gears. They're very well spaced. As the guy who sold it to me said, you could ride up a tree in first gear. And as I say, I can go downhill and get to 25 or 30 MPH and still be peddling to try to go faster in 8th gear.
I (obviously) have a helmet, and won't ride anywhere without it. I value my head, or what's left of it, too much for that. I also have a nifty little mirror (below) that is basically a rear-view mirror.
I like to keep myself safe. And 10 miles a day on a bike is really really good exercise. Considering that I'll probably be doing it 3 days a week for maybe 15 of the 16 weeks this semester, that's 450-480 miles on my bike. Awesomeness.