I am always very interested in shelving decisions (while routinely arguing with them) - for example, our local library has an area for mysteries which does not include certain categories of suspense fiction, and I'm never sure where to look for things. Certainly my books would be hard to shelve; they don't anchor strongly in the SF section either.

I like the idea that romance is about structure and focus and expectations - and that perhaps a book can be romance while at the same time not correlating with those elements - but it doesn't square with marketing in all cases. But of course an awful lot of "literary" fiction (and a lot of mysteries, etc.) might qualify as romance if you put your thumb on the scales a bit. Labels, pfft.