Update: In the past I recommended Yak Trax for the casual hiker. With less than 100 miles, these broke about 5 miles from the trail head on hard packed icy, hilly terrain. I now view these as a disposal product, and recommend keeping spares in your daypack and using this product for casual hiking and walking only. Recently, I have upgraded to Kahtoola Microspikes.
In the past I reported that hard packed ice and snow need not slow down the casual hiker. Lightweight Yaktrax for are relatively inexpensive and easy to use. Mine weigh 3.5 ounces (99 grams), making it easy and convenient to carry them in my camel back all winter long. Best of all, they can be used as a slip-stop with my soft trail runners. My Kahtoola Microspikes weigh in heavier at 11 ounces, but also work well with my soft trail runners.
For mountaineering or even hiking over over ice covered boulders, a spiked Crampon type assist is needed. But for casual winter hikes along footpaths meandering through forest, or even a walk in town, Yaktrax Walkers over waterproof trail runners provide comfortable slip prevention. My complaints? One seems to pop off for every 3 or 4 miles (4.8 to 6.4 km) hiked. Also, they appear to be disposable as the broke with less than 100 miles on them, so if this is your option of choice I suggest you keep a spare in your backpack.
For more information, check out my post on footwear for three season hiking and paddling adventures.