Let me explain them further:
A. Learning/self-betterment relates to what I expect the book to teach me, either by introducing me to something new (like say Marcus Aurelius' Meditations) or to expand my knowledge on something I have some idea about already (e.g. various pop-econ books I've accumulated through the years). It typically relates to non-fiction, though some works of fiction have probably gone a long way in helping me define my world-view as well.
B. Overall entertainment value relates mainly to how well-written a book is and/or how much the underlying ideas may tickle my mind. This usually helps when choosing what works of fiction to buy. It's worth considering since I rarely re-read books anyway, so a good writing style may leave as much or more of an impression than the plot (some of Wodehouse' lesser works provide good examples of style trumping plot by a fair distance).
C. My current attention span is defined by how busy I am, and what other books I might be reading at the same time. If I'm already reading something fairly heavy, I might consider picking up something that's easier on the mind, to read in the loo, say, or late at night before I finally go to sleep.
D. Signaling value is sometimes a factor, though I try not to give it too much weightage. this is basically related to deciding whether owning/showing off a book could affect other people's perceptions of me. Now that I have loads and loads of books at home, this isn't much of a concern when considering individual books, though sometimes I admit it can play a role when deciding what non-fiction to buy, in terms of 'if I take this book to office and leave it casually lying around my desk, will that make people think of me as an intellectual, or as a pretentious so-and-so?' Come to think of it, given that I did a Masters in Econ whereas most colleagues are engineers and/or MBAs, both the above views are probably held already, so the additional book won't shift opinions at the margin. This probably is a vestigial trait left over from having posed on main corr at various times in years past with a wide selection of books from the Stephen's library.
E. Cost-effectiveness - This may seem like a vaguely heretical idea for a lot of book-lovers, but every once in a while when deciding between 2 books, I end up considering which one offers greater bang for the buck, so to speak. So, for example, when Tom Friedman came out with 'The World is Flat', I figured that his 'The Lexus and the Olive Tree' was selling at a much cheaper price but still gave an introduction to the same broad set of ideas, and bought that instead. I got half-way through it, decided that he didn't really offer much in terms of points A,B or C above and only partially helped with D, and didn't bother reading any more of him. Saved myself some time and money in the process. Similarly, I've quite often considered picking up new pop-econ books only to leave them back on the shelf for a while until the cheaper paperback comes out. Admittedly, with my credit card and Flipkart at hand, I'm in danger of now being much more profligate.
Anyway, that was all prologue to what is really the point of this post. I've just signed up as a member of a library in my neighbourhood, and as a result it got me to thinking how this changes the way I choose what to read. Since the cost of membership has already been paid, I no longer have to worry about E so much, nor even D. I can instead choose to balance factors A, B and C, which I think is quite freeing. Since the fees are more easily perceived as a sunk cost in this case, I can opt to quit reading books without feeling guilty, and I can hopefully read across a wider range of genres that might interest me. At least, that is, until I run across cute women in the library whence the impulse for D might kick in and I suddenly reach for Kahlil Gibran.
Until that happens, I'm open to suggestions from loyal and not-so-loyal readers on stuff I ought to attempt reading . This might give you an idea of the stuff I typically tend to read, in case you're wondering. Drop a comment or two. I might even write about the books if I like (or dislike) them. I know, I've promised this before as well, but this time I really mean to do it. Dependent on points C and D above, of course.
Bonus book review: Sheena Iyengar's 'The Art of Choosing' is a good read if you're interested in topics related to choice, limited rationality, etc. all discussed with a certain amount of nuance and a few Indian anecdotes.