I found this book meme at In the Headlights and as it's about books I couldn't resist, being as I am an inveterate book hoarder.
Hardback or paperback: Depends. If I know I want to keep it as reference, or as part of "the collection" then usually hardback. If it is for general reading, bedtime reading, idle interest or for travel reading then paperback. It also depends what's available, especially as I often buy secondhand books.
Amazon or brick and mortar: Amazon, eBay or Abebooks. Not because I don't like real bookshops, I love them, and always seek them out when on holiday or visiting somewhere. But there are too new bookstores with too little range of stock of interest to me. And there also aren't that many secondhand bookshops around. I know they've died partly because of Amazon et al. but getting to a bookstore is a major problem given one's working hours etc.
Barnes and Noble or Border's: Neither; I'm on the wrong side of the big pond. Book bookstores like Waterstones (or whatever they're called this week) I find dull and boring. That's largely because I don't read much fiction and they just don't stock a decent range of non-fiction. If I come across something I want I tend to go in for instant gratification and order from Amazon for quick delivery. But I also keep a list of (mostly out of print) books I want and search for these when I get to a secondhand bookshop -- or even on eBay.
Bookmark or dog-ear: Always, always bookmark. I hate having books with dog-eared corners -- I'm afraid it's all part of the way I was brought up.
Alphabetize by author, alphabetize by subject, or random: None of those. Books are kept largely by subject, but not well sorted within subject -- except the history is largely in chronological order. And there are interesting categories too, like "books by people we know".
Keep, throw away or sell: Once read, or even if not completely read, books are kept. Books are a treasure trove. This is why we have a house full of books -- in fact they've taken over. Eventually as they become less mainstream (for us) they get relegated to behind the other books; and every few years we have a purge and dispose of ones we really no longer want: we might give them to friends (if they want them) or to the charity shop, or to a friend who does a car boot sale for his writer's circle, or sell them on eBay. Books don't get thrown away unless they are really, really beyond any use.
Keep the dust jacket or toss it: I always keep dustjackets; again part of my upbringing. They are part of the book, make useful substitute bookmarks and (if one cares about such things) enhance its future value. OTOH they irritate me when reading the book, so I often remove them temporarily.
Short story or novel: If I have to choose, novel. But I mostly read non-fiction.
Collection (same author) or anthology (different authors): I don't really know. I guess it depends. I can read either. It's more a question of reading what I fancy reading than worrying about artificial distinctions.
Harry Potter or Lemony Snicket: I've not read either. But I guess if I have to choose it would be Harry Potter. Or Terry Pratchett. Or Douglas Adams.
Stop reading when tired or at chapter breaks: Oh, stop at chapter (or at least section) breaks if I can manage to stay awake -- not always possible!
"It was a dark and storm night" or "once upon a time?": Don't care. I don't read a lot of fiction so it doesn't matter. It's more a case of whether the book interests me.
Buy or borrow: Buy; always. I never borrow books and I never lend books. If I want to read something I'll buy it; after all I may well want to keep it and read it again or refer back to it.
New or used: Either. Not everything I want is available new; and some of the old books I want are cheaper in reprints than secondhand. Also factor in that there are books I would like to look at and can often pick up cheaply on eBay rather than having to pay full price.
Buying choice: How do I choose what to read? Usually either books I come across by chance, or I want a book on a particular subject, or they're get recommended/mentioned to me by friends. I seldom read book reviews, and even less often use them as a source of information.
Tidy endings or cliffhangers: I'm organised, so I prefer tidy endings; except when I don't.
Morning reading, afternoon reading, or nighttime reading: Whenever I can. Which usually means a few minutes in bed at night or when I'm ill. So I don't actually get through a lot of reading, something which is made worse by being a slow reader.
Stand-alone or series: Not bothered. But see previous comments on fiction vs non-fiction.
Favorite series: Anthony Powell's A Dance to the Music of Time -- now what did you really expect me to say? Do Lewis Carroll's two Alice in Wonderland books count as a series? Then there's Douglas Adams's Hitch-Hikers Guide to the Galaxy.
That's all, except that, inevitably, TAG, you're it. If you enjoyed this, please perpetuate the meme and comment here so we can all enjoy your answers. I'd like to see Jilly and Kelly take up the challenge. I'd add Noreen and JohnMon as well but I've yet not persuaded them to get weblogs (hah; chicken!).