Our shelves are full enough that it can be hard to place a new book. I look at shelves in the office upstairs, and see a number of books that I don't think we need to keep, but which I do think I should probably read before we get rid of them. In most cases they were presents, and I remember who gave them to me, and sometimes remember for which birthday or on which Christmas. It seems to me that I will have done my duty by the givers if I read the books.
So next week, when the current bus book is done, I will devote my commute to making space on the shelves. In all, there are six or eight books due for this treatment. One more might qualify, but is awfully heavy. Carpe Librum will accept them and might be able to sell them.
The last book that I read to get rid of was Perry Miller's The New England Mind: The Seventeenth Century. It was not bus reading, requiring as it did too much concentration. I read it mostly sitting on the couch, and gave it away. The friend who took it must have backlogs of his own; I have never asked whether he read it.