I too have sold on cash4books in the past, and like a PP, found it not to be worth the effort, since so few of my books netted me any cash. Plus a few of the books I sent in, were not accepted after all, due to minor issues with the condidtion of the book.
I do sell on Half.com, but as you mentioned, it's a much longer process for the book to sell, but I have a closet that I store my listed books in and once a year clean out the closet and send them all to goodwill or the like. Furthermore, I only sell books on half.com that will bring in at least $3, if it's listed lower than $3 sale price on half, I send it to the thrift store immediately.
I also will list those thrift store boun books on paperbackswap.com, but it just gets you a credit for a future book, but have a list wish set up, so have received many books I wanted thru the site, with little effort on my part. However, I don't ever request fiction, almost always some sort of an educational book that I want, canning, gardening, health, etc are the topics I gather over fiction which is the most prevelant on paperbackswap.