Might be a fad but I love mine, I have a spinal condition that makes standing for (most) of the day much less than painful than sitting. (so I built myself one to solve all the usual problems, 21sq/ft of space, goes high enough to be suitable for non-midges, completely and totally stable, in hindsight I might have got carried away a bit http://imgur.com/a/H7fxb - the chair is in the process of been replaced with a stool (that I'm also building))
They're terrible chairs. A mesh back is nice but you need a proper seat. The Aeron cuts off circulation to the legs. It's also about 5x overpriced. I just upgraded to a low end model from a no-name brand. [1] It's honestly a better chair.
Well it is the product of a world class design firm. Even if it was a mistake to have a mesh seat they got most everything else right. But it's telling that the Herman Miller Embody (successor to Aeron) has a real seat.
Sounds like you might have gotten the wrong size. I used to do 12-13 hours sat in one of those at the office, with only a short break during the day to grab a snack, and never had any problems.
I didn't mean to sound contradictory. I actually sold mine on Craigslist! But a spike in Aeron chair sales may not imply that a bubble is popping. It might just be that startups got off the bandwagon and decided to care about their sorry butts. Literally.