I appreciate the pragmatic approach here. "Is this the best tool for the job?" is exactly the right question. The welcome trend toward minimalist footwear has been, disappointingly, shrouded in philosophy and thin references to science. The issue of backpacking footwear need not be philosophical, unless of course you hike for primarily philosophical reasons. I hike more for pleasure than to connect with my ancestors, or as a testament to human evolution, so whatever keeps me in pleasure and out of pain is what stays on my feet. Also, while studies can point us in the right direction, personal biomechanics and environmental factors are so particular, that your own 'scientific experimentation' (i.e. experience) provides the best info. I find online anecdotes, minus the zealotry, helpful as well.
My own anecdotes:
Dancing around in super minimal shoes like Merrell trail gloves has been a joy on the short, well traveled, technical trails here in the boulder foothills. As a bonus, its improved my strength and agility. I also used these section hiking the CT last summer averaging 25-30 miles a day with a wet weight between 8-12 lbs. While a more gentle gait left me fresher at day's end, I bruised my feet pretty bad after a prolonged night hike. I wore these again on scrambling missions early this summer, and while great for smearing and boulder hopping, one wrong talus step taught me they're not the tool for the job. I concur with ryan on this: the super minimal shoes are best for shorter on trail hikes in good daylight.
A fairly committing 5th class scramble in MT101's early in the summer had me searching out a minimalist shoe with mild protection that bridges running and approach styles. (wow, we certainly can afford to be finicky consumers these days!) Two shoes that fit bill are the scarpa spark and the la sportiva vertical K. Both have phenomenal grip. The vertical K basically gloms onto rock, wet or dry. Imagine having gecko feet. At first I was resistant to these, since the morpho cushioning didn't settle well with the minimalist kool-aid I'd been drinking. That said, no shoe left me feeling better after long trail miles, and non-performed as well on technical terrain from scrambling to talus/boulder hopping and side hilling. The morpho cushioning actually resulted in less ankle strain on prolonged side hilling. My gripes: the toe box isn't wide enough, the forefoot could use a touch more protection, and they dry too slow for being such a light shoe. All of these gripes are addressed in the helios, coming out in the spring. The spark felt pretty ideal on a few day hikes, but hurt my knees after long miles. Not sure why this is, but could be related to having to readjust after using the cushy vertical k's.
And most recently, I've been wearing merrell mix masters. These are the most comfortable semi-minimal shoes I've tried. I generally put these on and forget about them, which is a high compliment. The sole offers a good amount of protection without too much cushioning. Its sort of like a more comfortable MT101, with less drop and better grip. Close to my perfect for trail shoe, actually. That said, I got pretty used to the grip and agility of the vertical k's, and in comparison, these can sometimes feel clownish and rigid. My friend and I recently did an overnight in zion w/ stretches of slick rock scrambling, and more than a few times I missed the grip of the vertical k's. (finicky indeed ;) But if I were thru-hiking a long trail, I'd stock up on these for sure.
Last note, I wanted to like the lone peaks. I love the wide toe box, but I had to choke my midfoot to get a decent performance fit and to keep my heels from slipping. The shoe is also fairly rectangular shaped, which did't really feel anatomical to me. That, combined with the clunky and overly rigid soles made me feel like I was wearing wooden planks on my feet. Not a bad trail shoe though, and the construction is bomber. These didn't fit my particular feet well, but another reason why personal experience is the best criteria. I can totally see a bunch of people going all RJ groupie and buying Altras after reading this. Runners warehouse is a good bet, with their return policy.
Wow, didn't mean to write an e-tome, but I guess this is a decent place for such an anecdotal purge. BTW, psyched about RJ's analytical and practical articles of late. A big reason I started reading BPL.