I am by no means in the same class as any of the awesome hikers above when it comes to total trail miles.
Later this year I will be attempting a 400 mile thru-hike with a sub 4-pound BPW setup. Longest stretch w/o resupply will be 8 days, so the first few days of that is gonna suck as the weight of food will be 3x more than my BPW, but such as it is.
I did a little over 500 miles in 2011 with a 4.4 pound setup and another 250 with a sub 2 pound setup.
Realistically though anything under around 4.8 pounds is where it starts getting really hard to do a thru-hike without suffering.
>>> What worked?
No-cook eating. Easily save a significant amount of weight just in food packaging by going over to no cook eating. Basically end up with two or three bags of food, rather than a bunch of different bags of different meals. Also save a significant amount of weight over the entire thru-hike on fuel dead weight. Anymore I make a cup of warm tea at night with half an esbit and that is usually it.
Tarps. Or an insanely light shelter. Last year I did most of my miles with a tarp but for this trip I will be taking a sub 1 pound TSW setup for full bug protection.
High quality cloths. I decided to go the route of going with high quality cloths and putting a lot of trust in a layering system. So far it has worked out.
High risk water treatment. In other words, none. Thankfully I live somewhere that I pretty much never have to treat water. For my hopeful hike later this year I will also not be treating water, so that saves you around 3oz. High risk for 3oz though.
No Stuff sacks. Really, the most stupid thing ever. I see some guys with stuff sacks for this, stuff sacks for that, and stuff sacks for their stuff sacks. I carry a single stuff sack that pretty much everything except my shelter and bag and cloths go into. DRW protects your bag from the rain, shelter does not need protection, and cloths usually go into a big zip-lock bag (which also gets used to clean cloths with a micro-dropper of bleach, and serves as a pillow at night).
The lightest pad, if one at all. I use a GG 1/8th pad. It really does nothing to help me with comfort but it does wonders to give my backpack some rigidity. Could still carry a Zlite and be under 5 pounds.
>>> What did not work?
Shoes that do not fit you properly.
>>> Neatest trick I have learned from other SUL/XUL thru-hikers:
The power of Sealskinz Waterproof Mid-Calf socks when it gets cold. Screw using these to keep your feet dry (that is impossible) but these suckers trap heat inside of them and easily increases your foot temperature a few degrees when you need it most. Mine are 178 grams and I do not think twice about having them in my shoulder/winter gear - not even for a microsecond.
John B. Abela