I usually check out an interesting book from the library as soon as I hear about it. If it turns out not to be my type of book, then I just send it back. Sometimes I end up with several books that I really want to read and I hold onto them way too long in an attempt to finish them all. This happens all year long. By my best guess, I could probably buy 10 books a year with the library fines I pay. That defeats the purpose of borrowing books rather than owning them.
One reason I tend to hold onto the books is that I'm afraid I will forget the titles once I send them back. Keeping lists of books I want to read has not worked for me. I lose the paper or file where I have the list. I'm hoping that the new account I set up at Goodreads will help me with that. I had the same problem with keeping track of my needlework projects, and Ravelry has been a big help with that. Somehow, the online and social aspects seem to work better for me. I know that in the case of Ravelry, it has inspired me to actually knit more. Hopefully, that will be the case with Goodreads. At least I'll rack up fewer library fees.