Snow_Dog wrote on Apr 21^st, 2010 at 2:38pm:

You're a lot more likely to get sick from poor campsite hygiene than from drinking untreated water.  Giardia originally came from people, not beavers.  People are still the source you are most likely to pick it up from, too. Just pay attention to where you get your water and you can leave the expensive, easily compromised filtering equipment at home.  I bring a bottle of treatment tablets just in case I am unable to get water from a source which meets my minimal standards. That said, there's no way you'll get me to drink from Lakes 1-4 and several other insanely popular lakes without treating the water.  I don't fear the beavers too much.  I fear the two-legged disease carriers much worse.

I'll concur with Snow_Dog.  I just make sure that I'm filling my water containers some distance from shore, unless the dipped water is going to be boiled before use/consumption.  That said, I can think of no place in the lower-48 where I'd choose not to filter unless the water was coming directly from a spring.

I did decide to try the Katadyn Base Camp filter a couple of seasons ago (mostly because I was traveling with other "new" companions).  It was a reasonably easy "swap" since I had been using a comparably-sized dry bag for that purpose (the one I use if from Cabela's and has an air-bleed valve at one end ... or should I say a water spigot).  The Base Camp worked well at the beginning of the trip, but I did notice a slow down before the 2-week trip ended.  Being that the trip was in late May/early June, I'd guess the filter started to become clogged with pollen ... which seems to be everywhere that time of year.  

I did take the filter on 2-3 trips, but I'm now back to my former technique for "far-north" traveling.

One should also note that things like Giardia CAN BE acquired through activities other than drinking water ... like bathing and swimming.  So a bit of caution should be exercised when doing these activities (unless you swim without stirring up bottom sediments ::)).

dd