Great to hear others getting same mileage as me - my late 2012 Air bought in March 2013 still going strong with only a battery replacement done so far. 4Gb RAM, 128 Gb SSD. Used daily for browsing, watching videos online, building IOT software, playing with unikernels. The only time it hasnt performed was when used last year as a work machine while waiting for macbook to arrive - and that was down to the collection of corporate stuff required. Once got new work machine, i removed all the work stuff, and the Air went back to being the solid daily hack it has always been. In the same time my friends with other laptops have had several cycles.
It's largely turned into a doorstop after the battery was dying a year or so ago. I bought a $70 battery from a random seller on advice from a friend who had good luck with fit and instructions. Replacement was a breeze, and it seemed great at first, but pretty quickly started just dying on me. I use the laptop so rarely, it just seems like, no matter what the SOC was last time I used it, next time I pick it up (usually a week or more later), it was dead and needed power.
that said, about a year or two ago was also when it just started feeling too slow to be usable (beachballs all the time). I blame web bloat, mostly :-/
I bought it new, so I definitely got my money's worth out of it.
My work won't be processor intensive, just a personal machine. But given how long I kept my old one, I intend to keep this one for a long time, and I'm not sure where the best price:performance tradeoff is. I could argue going low-end and replacing it sooner, or high end, and keeping it forever.