I have been considering doing this myself. It would be attached to my front fence on my footpath.
I often leave free things on my footpath with a sign. The items are taken relatively quickly and I have never spoken to the people who take them. One person left a note and some cash when I had lots of one type of plant out.
I have been keeping an eye out for a suitable cabinet that would protect the books from the weather, but with glass so they could be seen.
I would like two cabinets, so I could put children's books in the lower one,
I think it is a great idea, but having one on my property, and having a variety of strangers coming there on a regular basis, is not really appropriate for a family home. Our local community houses and neighbourhood houses have them for all to experience the joys of reading. I have seen one at a homeless shelter. I know if I was homeless, I would still enjoy a good book.
I only recently heard of these street libraries throug a Weekend Notes article by Paula McManus about some in Adelaide. They are in public places and that makes good sense. I can see real value for them at community centres, council offices, and churches. I'd be happy to have one in front of my property but as we live in a closed court I'm not sure it would suit.
I think it is a really lovely idea. But I also think it depends on the area you live in.
My street doesn't get a lot of traffic and I don't think my neighbours would appreciate people coming to visit my "library"