There seems to be increased interest in POD sites as we become ever gloomier about microstock

I spent some time with Zazzle, made a few sales, but it mostly went nowhere. Unless you have a way of promoting yourself, you're just putting your needles in another giant haystack. And their prices for things like shirts and mugs are, I think, too high.
But for me, the main problem with Zazzle is the site itself, and the tools it provides for creating products; it's just way too slow and tedious. And the only way you make anything at Zazzle is by creating lots and lots of different products from each image.
Others, who have more salable material, more patience, and/or some self-promotion skills, may give you a more optimistic assessment.