When in the market for new footwear, it is imperative that you find a model that is right for you. The model must compliment the shape of your foot, the height of your arch, the way in which you transition from heel to toe, among other things. It must offer adequate support and cushion given the strength of your feet and ankles, and the weight of your pack. It must be appropriate for the conditions in which you intend to use it, in terms of breathability, forefoot protection, water-resistance, warmth, etc. Lastly, it must satisfy your preferences as far as weight, style, and price.
In Spring 2007 GoLite launched a revolutionary line of trail running shoes that also work really well for lightweight backpacking. I would encourage you to check them out at GoLite-Footwear.com
For most of the year I wear trail running shoes, not hiking boots as would be expected. The reason is that, compared to boots, trail running shoes are:
During most 3-season conditions I wear non-waterproof shoes because shoes with "waterproof-breathable" membranes are heavier, less breathable, and hotter than their non-waterproof counterparts; moreover, they take longer to dry. Plus, I have yet to hear about a "waterproof" shoe that actually is -- when I am hiking in prolonged rain or in a persistently wet environment, water is going to find a way in, usually by coming in over the top. The most ideal running shoes become, then, those that squeegee water best and dry the fastest, and with few exceptions non-waterproof shoes will be better in doing this.
There are a few situations in which I advocate the use of different footwear. One such case is when there is enough snow on the ground to get your feet wet, and cold enough temperatures to make this uncomfortable. In this case a waterproof shoe is desirable -- like a full leather boot or a running shoe with a waterproof-breathable membrane; a gaiter can be added for additional protection. While waterproof-breathable footwear fails in wet environments, in this instance they should work, since snow is drier and easier to protect against.
In extremely cold environments, I introduce into my system a neoprene overboot, which I wear over my running shoes and oftentimes with snowshoes or crampons. The overboot provides excellent insulation, a built-in gaiter, and adequate protection from the cold dry snow. Check out the Light Energy overboots from Forty Below.