Actually, they have shown their appreciation of my work on more than one occasion. I first worked there for about 6 months, then resigned to go off on my little Lake District jaunt. After I had been back a while, I got a call from them asking if I'd like to go back (hadn't been able to find anything else in that time). My line manager said they'd tried a number of people in my absence, but weren't happy with any of them. Even though I only do a 4 day week now, it seems they're still really happy with my workload, my colleague thinks I'm their "golden boy" and he's been there a lot longer than me!
So far, they've also been quite understanding with the amount of sick-time I've had to take, so really, I feel I'm in a pretty good situation. Just want to keep it that way.