I've now received several inquiries, one recently, from people who viewed my work on Flickr and inquired about permission to use an image. One of these was quite polite, and respectable, and provided enough information to verify that indeed, the person requesting could do what they said they could. None of them offered to pay. That polite one? Politely described that the budget didn't allow for pay-for-use, and when I explained why I consider my work to be pay-for-use, also replied and politely removed my name for their request list.
The other two... not so much. But you know, silence is in these instances an acceptable response to being informed that no, free use of my work isn't actually such a compliment as all that.
So, now I've adjusted my profile information on Flickr to state that my work is available on a pay-for-use basis. Because, you see, since I've sold prints of several of those images to people, it is hardly fair for someone else to get the use of them for free.
Also, my feet are currently being caressed by the gently twitching paws of a dreaming Border Collie.