I used to use an MSR MiniWorks (about a pound). I got into an ultralight phase and started using Aqua Mira drops (3oz), which are the ones where you mix A+B, wait 5 minutes, add to the water, wait 20 minutes, and drink. That worked fine, without the physical effort, but with the down side of having to mix and wait. i kept hearing about how awful iodine tasted, but one day, while standing at an outfitters checkout, i saw some polar pure sitting there and bought it. SO glad i did. it's already at saturation, and you just have to add it to the untreated water. there is a slight taste, but i don't mind it, and after a week on the stuff last year, i find that i pretty much can't taste anything bad anymore... it took about 2 days that first time, and now it's ok after the 2nd bottle (about 2 hours into a trip!).
I carry two 32 oz bottles. one is "drinking", the other is "working". as soon as i finish a bottle, i pour in the correct amount of polar pure, dunk my bottle under the water (keeps the surface crud from getting in), fill it, and cap it. this then goes back into my pack and i drink from the other bottle. shampoo, rinse, repeat... you get the idea.
when i get to a portage, i drink everything i have and then portage without the additional 4 lbs of water. longest portage to date is 1.6 miles or so, for which i think i carried a full bottle to start. again, you get the idea...
polar pure is off the market over an issue with the DEA, but there's a canadian supplier of sublimated iodine crystals that i've heard on another forum provides good service.
http://raems.com/webad/USP.html i believe the owner's name is Brian.