I had posted the method before, and nobody picked up on it. I think it's probably the most powerful way of storing crops in Photoshop files; they're very compact and, as you say, alternate crops are easily created and added to the files, adding no more than a couple of KBytes each.
I'd say that paths are probably a very under-used feature of Photoshop, but they provide a lot of power, too. Paths are particularly of importance when working with InDesign, as you can set up the clipping path for an image in Photoshop before linking the Photoshop file to an InDesign document.
However, I find myself using paths for other tasks as well - possibly because I'm familiar with the way paths work in Illustrator and Corel Draw. For example, when masking certain shapes with a fairly regular border, I've found myself turning my selection from my favourite selection tool (be it the Lasso or something like GrowCut) into a path via Make Work Path From Selection (if you hold down Alt when clicking the option you can choose the accuracy, which tunes the number of control points) and editing the path to a finished selection using the Direct Selection tool.
Indeed, if you're working in a path based mindset, you use the Pen and Freeform Pen tools instead of the Lasso, because they can create paths directly. Unfortunately there's no Magnetic Pen equivalent of the Magnetic Lasso, which is useful sometimes.
Another potentially underrated feature is layer effects, but that's a whole other story (apart from noting its use for framing and framing scripts - Mike's Framer makes heavy use of layer effects).
David