I've accidently picked up a walking habit. I get up around 6am and walk a couple miles around my neighborhood while listening to podcasts of This American Life, The Moth, or the occasional talk from Zencast. I cover 2-2.5 miles each time.
(This isn't a new year's resolution or anything, I just like being alone. It is probably decent exercise, though.)
When I realized this habit had come upon me, I desired to gather some data (of course). I know myself well enough to know I couldn't be too involved in futzing with a new device, and I really didn't need a new one. I have a Samsung Captivate phone ($60! I rule the frugal!) that runs Droid and I don't need yet another device.
I was interested in the ability to track my walks, and upload and tabulate everything. When I read that some of these devices also tracked sleep, I was more interested. I'm often a very light sleeper and am interested in improving my sleep at this point in my life.
The FitBit seemed to get good reviews for tracking sleep, but I wasn't hearing from actual users. I asked on Facebook and the wife of a friend gave me a personal review of her FitBit, and how it's recorded her sleep data very poorly. I confirmed this with several people on the FitBit forums. There seems to be some class of people for whom that feature is not working well. (It seems to be a great exercise tracker though.)
Since I really didn't want to spend $100+ anyway (that's another show stopper) I started looking at the app store. I found two products that seem well loved: Endomondo and SportyPal. I really liked SportyPal and went ahead and downloaded it. It took a little work to figure out that I had to download an app specifically to make the GPS in my phone work better for stuff like this, but the results are great and the app's price is right.
You can see an example of one of my runs before I figured out how to boost the performance of the GPS chip here. After I figured out you need to run a booster program for the GPS chip, the lines get quite a bit smoother and more accurate, like here. It's pretty simple. You turn it on at the beginning of your walk, and turn it off afterwards. It works for walking, running, biking, waterskiing, all sorts of stuff that you can track by distance. It also tracks work inside the gym, but I'm not interested in that.
If you're curious about such things, you might really enjoy downloading it and trying it out. It's a pretty app.