I then made a very half-hearted stab at finding the pink cubes, but I didn't really enjoy myself, so I went ahead and tried some speed runs.
My first attempt was 144 minutes. I got stuck trying to solve a chamber with the green gun that I had previously visited only after I got they yellow gun (the order in which I visited and and solved the chambers on my first playthrough was pretty random). My second attempt was 91 minutes, a substantial improvement, though I still wasted a lot of time by forgetting the proper route. I think I could probably shave off another half hour at least if I could avoid those little mistakes and actually learned to climb the tower to the red gun in a halfway efficient manner.
That'd still put me nowhere near the first class of Antichamber speedrunners, who can do it in less than three minutes:
Very impressive, though it looks like going so fast involves exploiting glitches and that's not really my scene (on the other hand, with a game like this, it's hard to distinguish between glitches and "emergent gameplay.")
My final verdict is that this game is amazing, I'm glad I played it, and I highly recommend it to anyone who hasn't experienced it before, but I can't sugar-coat the past - there were times when it made me absolutely miserable. Granted, a significant portion of that can be blamed on my own carelessness (plus, speedrunning taught me that the main path is actually pretty straightforward when you don't stop to explore every damned side-path in the game), but I think I can't discount the fact that this game is simply a poor fit for my personal preferences - I like knowing the rules, and while I've been known to enjoy going off the beaten path from time to time, a game, like Antichamber that is pretty much all off the beaten path is just a little too much responsibility for me to handle.