I have been running on YakTrax since Christmastime a year ago, when I received the YakTrax Pro as a gift (from the Enthusiast, who in turn has gotten her own pair this year). I wore them throughout the end of December 2008 to early March 2009 and now what little I have run this year.
YakTrax offers two varieties of traction devices, the Walker and the Pro. You want the Pro for running.
The YakTrax are primarily made of rubber with a steel coil on the bottom for traction and a Velcro strap to secure the fit over your running shoes (or any other shoes). The easy on-off is a huge benefit for times when you think you need extra traction, but it turns out you don't. Even mid-run, you can pop 'em off, fold 'em in half and carry 'em back home.
I have run on everything winter throws at us in Northeast Ohio, including new fluffy snow, hard compacted snow, wet slush and ice patches and on deeply covered trail paths or lightly frosted roads. My footing always feels secure unless I step on a patch of plain wet asphalt--and watch out for manhole covers. The YakTrax do add a bit of weight to your feet, which you will have to get used to, but running in the snow is already more difficult.
YakTrax Pro MSRP is $30, but you can easily find them for $20 or less online. I estimate I've run 40 miles in them so far, and some of that has been on less than ideal terrain (i.e., pavement, asphalt ... not snow). I expect to get at least another season with this pair, and I'd say that's a good deal. (Steve Stenzel blew out a pair of YakTrax after two seasons, but he runs a hell of a lot more than you and I do.)
For the cost and overall functionality, it's hard to beat YakTrax.
Booze Hound Rating: 4 fingers, neat
[Drunkard's note: The Booze Hound rating system is based on a good pour. Up to five fingers, either "on the rocks" or "neat." If you can't figure out what's good and what's bad, you need to spend more time drinking.]