Just to give equal time to the "Dip and Drink" people...

It really doesn't matter to me whether you carry a filter or treat your water or do nothing, but here is some worthwhile reading from old discussions:

    Water and Giardia around Mt. Whitney (especially the 60000 liters part)
      and
    Filter question

I have hiked nearly all the JMT without treating the water. It is quite a feeling of freedom to carry the old metal cup, and just dip the water and drink. My pack is lighter, and water stops are simpler and more frequent. Since filtering is not an issue, I don't carry a filter, and I don't carry a load of water (Whitney area above 12k is an exception). The next water stop is usually just a short distance up the trail.