I had the good fortune to handle TWO Buck/Mayos on Saturday, one at Knife Expo '03 and my own when it arrived! Another plug for Larry: he's a great guy to deal with.
My first reaction when I picked up the display piece was, "Wow, this thing is light!" At less than 3 oz, it's comparable to my Victorinox Soldier in heft. The show knife was flawless, as to be expected, with very smooth action and secure lockup. No finish or grind errors at all.
I scrutinized my own Buck/Mayo when it arrived and am delighted with it. The high hollow grind and thinly-ground edge makes it an extremely efficient cutter for most materials. Make no mistake: this is no prying tool, nor is it a heavy-duty folder. I have faith in S30V, but even fantastic steel and heat treat can't overcome a geometry unsuited for extreme work. I measured my blade at a hair over 3 1/8", tip to scale. No blade play vertically or horizontally when locked.
Okay now for a few nit-picky things: I agree with Larry about the electro-etched logos. They look fine from a distance but close up they're not very 'clean' and precise. Stamped or laser-etched would be great. Near the base of the edge I found a speck of scale that the polisher missed. No problem, just rubbed some CrO compound with a q-tip and it's gone. The inside of the opening hole is kinda rough, so I took some 100-grit SiC powder on a moistened q-tip to smooth it out some. (If you try this be very, very careful not to get any SiC in the pivot, or you will hear a sickening grinding sound when you open/close the knife!)
The lockup is tight, but the locking bar only engages the tang about 60%. More contact would be nice but I'm not worried, breaking the knife in and eventual wear should move the bar over in time. The handle scales are machined very well, with no unsightly tool marks or errors. Even the edges of the holes are chamfered nicely. The pocket clip is slim and TIGHT. I have a really hard time clipping the knife to jeans and even khakis. The clip is positioned perfectly between the slot for the frame lock and the holes on that side. Very unobtrusive, as Rob19 pointed out, and does not interfere with reinforcing the frame lock.
The action on my 172 was not as smooth as the display model I handled at the show. The beginning of the opening stroke was smooth, but it got a bit rough about halfway open. Cycling the knife should smooth it out. Buck uses a thicker, gel-like lubricant that makes the action feel more fluid. I felt this on their Alpha folder also. The washers are very thin and almost impossible to see. Using a very bright light, it appeared to me that one is white and the other is copper-colored. I asked the Buck rep and he said that Buck is moving towards bronze washers, but he didn't know about the 172 for sure.
I took a risk and flushed out all of the original lube with Gunscrubber. Now the action was rough the entire stroke. I heated the joint with a hairdryer and applied some Militec-1. I could immediately tell that the blade opened easier, as if I had loosened the pivot. This week I'll be reapplying Militec several more times to see how smooth I can get it. The stuff has done wonders for my BM Axis AFCK and my friend's Emerson Specwar, and I know it takes a few applications to get it really smooth.
The perfectionists out there will not find Sebenza-like QC but the 172 has all the right elements to excel as an EDC cutting tool: excellent steel, heat treat, and blade geometry, lightweight handle, solid lockup, smooth action, and fit & finish that most production folders can't match. And if I may say so, this is simply one SEXY knife

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Look, it's designed by Tom Mayo and executed by Buck. What more needs to be said?
