Stupid me. I have been trying for about a decade now to figure out a secure, efficient way to keep track of the books I have read. Not once, in all that time, did it ever occur to me to just search for an online service that specializes in precisely that. In fact, there are at least three major ones.
I have chosen LibraryThing, since it looks to be the site built most around cataloging, and least around social networking. Now I just have to remember all of the books I have read. So far, I have recalled 1062 of them. I know I'm missing at least another 500, even with my decision to exclude most works of fiction. Anyway, LibraryThing—do it.