I have access to 3 public libraries because of where I live, work and where my hubby works. Mississauga, Burlington & Toronto. I'm not going to pretend to be knowledgable about ebook library usage over dead tree library usage but I can say that there are a lot of books I've been reading from the library and when you consider that some books have 40 patrons on a waiting list, I'd say that's a lot.
The last bunch of books I've read were library books. They're not books I want to own but am interested in reading so the library is perfect! Eat, Pray, Love had a very big waiting list. The same for the Nicholas Flamel series from Michael Scott for instance. The first book has a list of over 40 people waiting for it in Toronto.
Toronto is clearly a bigger city than the other two I belong to but I find it interesting that Burlington, a smaller city than Mississauga, has a better selection of books and a longer lending period than Mississauga. Mississauga's max period is two weeks whereas the other two are three weeks. Burlington often has books that have huge waiting lists in Toronto who has more copies and sometimes has a book that the Toronto library doesn't. Mississauga's ebook library is apparently fairly new so it's much smaller than the other two but I borrow from there to let them know that there are people out there who use it.
I don't know how much it will impact which ereader someone will buy but I can say that it did for me. I was never sure I'd use the library feature or not but I'd rather have bought a reader that could do it if I decided to use the library than to not have it if I decided to. And it is something that I'm happily using and will continue to use as long as it's available.