I like my water filtered. I carried the MiniWorks EX from MSR on the whole A.T. I consider it a little luxury on a long trail, because it's heavier than some other water treatment methods(chemical, salt, light). If you don't treat your water at all, you should expect to get sick at least once.
With a filter, I get clean, great tasting water, without "floaties". I would say 80% of the water on the A.T., I didn't worry about. But for the other 20%, I was glad to have the filter. On one long hot day, with little water available, I came across a styrofoam cooler left by a trail angel. To my great disappointment, the cooler was empty, save for a couple inches of water that used to be ice. So, I whipped out my trusty filter and pumped a liter of water, that tasted fantastic.
Needless to say, I was excited when MSR came out with the new HyperFlow, which weighs about half what the MiniWorks weighed. Instead of the ceramic and carbon filter on the MiniWorks, it uses Hollow Fiber Technology(picture a bundle of micro straws), to filter water faster with less weight. The time it would take to pump water on my older filter was a drawback. You do have to backflush the filter occasionally, which seems an easy thing to do. One feature I really like is the ability to screw the filter onto a Nalgene bottle.
