I still go to used bookshops- but increasingly the little stores are listing their books with Abebooks, Bookfinders, Alibris, etc. I go online and check the offers, and sometimes find the book listed by a local. I phone and reserve it for pick-up. Saves the postage if close by.
Online shopping is also good for cds and tapes, many used ones listed by dealers.

Why leave my nice warm house when shopping can be done by internet and the purchase delivered to my door?