I think for me the biggest thing I have changed in the past 4 years are:
#1 - If I'm not comfortable sleeping, my trip isn't comfortable. Therefore 1/4 inch ground pads and the like are out. Being broad shouldered and a side sleeper, bivies and 3/4 length pads are out. I've finally settled in with a Big Agnes IAC. I tried the NEO and I just didn't find it as comfortable. That extra 10 ounces is wroth it to me to be comfortable sleeping.
#2 - I used to be filter only, regardless. After trying several types of drops and tabs, and methods for pre-filtering floaties, I am comfortable using either system and since being in Montana now for past 2 1/2 years, I have been using chemical treatments mostly. Although, if we go back east, I take the filter ;)
#3 - Trail Runners vs. Boots. I haven't bought a pair of boots now in 4 years. I'm a firm believer in trail runners but admittedly, always seem in a constant battle to find the right ones that fit me well.
#4 - Bags versus Quilts - It took a few tries, and over the past 4 years I sewed several quilts for myself, but I finally figured out a quilt system that is comfortable for me and I have used it to modify a Jacks R Better Springer quilt
#5 - I have been unwilling to change packs. I am using a 4 1/2 pound Osprey Aether 70 as both a summer and winter pack. Alot of times I leave the top pack behind which reduces weight a half pound, but I love the comfort and adjustability. And because I'm a big guy, a couple pounds extra doesn't really bother me. I am willing to try new packs, but I am rough on packs and the ultralight silnylon and that variety are definitely not for me. The new BPL pack looks interesting to me but I have a feeling it's price range is not going to be to my liking. If it's under 250, I may consider spending the dough to try it.
Last Thing - Canister versus Alcohol. I have learned that if I am out anymore than a night, I want my canister stove. Period. Seems like every time I go for multi-day trips with alcohol, I always under estimate or over estimate my fuel usage. With my canisters, I weigh them before and after each trip and mark the weights on the cans. I always know how far that fuel will take me.
All in all my venture into better eating, lighter packing has been a good one and I have enjoyed the tips and tricks I have gotten here from BPL members and from the BPL articles. It's helped me changed my mind several times about how we do things..