In the vein of the FRA thing only more so, AMS supposedly has servicing available, though I only have heard of it through Jay Leno jokes.

More commonly, though, I tend to bring along PC and other magazines with subscriptions I've bought with miles (or $3-4 a year on the subscription sites) and never get around to reading otherwise. PC ones are useful because you can rip pages with anything useful and toss/recycle or leave the rest.

Anything financial that relates to trip cost is ideal for airport time. I always do a cost sheet for personal trips (total air, hotel, car, other "base" expenses, then personal discretionaries), and it's perfect for airport wait times on the return.

As for specific locations, MSP is really excellent for getting on the train to the Mall of America and back (do-able in the 4-hour layover window). In BOS I always try to get a meal at Legal's Seafood. CO's island hopper through Micronesia used to be good for walking around before they got really bad about security, post-9/11 (though I'd think Pohnpei would be near the bottom of any terrorist target list).

A number of other airports are playable for longer layovers (4-12 hours, say) if they have train access or are close enough to other things so that the bus service is a chip shot.