No, this isn't a posting where I advise you to stop living through your books and instead get out there and live in the real world. That's crazy talk. Rather this is a posting where I walk you through the guidelines of when it is time to just put the book down and call it quits.
I used to have a rule with myself, that all books started by me, must be finished by me. It took me a long time to break myself of that habit, and many wasted hours that could of been spent reading better material. I think that the turning point for myself was when I started reading more of the classics. As I have stated previously, I am a self proclaimed book snob, and I blame it all on the very first classic that I ever picked up.
Being a book snob isn't necessary a bad thing however. I can instantly judge a book by the description given either on the back of the book or on the inside of the dust jacket. Is this a book that I want to read? Never judge a book by its cover, but totally judge a book by its description (but we all know that the cover is the first thing that grabs your eye when book browsing, so you do totally judge a book by its cover). If that method fails me, then I can usually tell if a book is a worthwhile read within the first chapter, sometimes the really poorly constructed books are quick one pager judgments. Usually it doesn't pass my writing standards, simply put. But sometimes the writing passes under my radar and it is the story line that is the disappointment. When this happens, just let it go (yes, I just did that). Put the book down. In really desperate cases burn it, use it for toilet paper, add it to your compost heap, whatever you've got to do to erase the atrociousness from your eyes, and your mind. I usually don't abide with burning books, or the soiling and destruction of books, but lets all just admit here that some books never should of been published in the first place (*cough*) so maybe we are literature heroes, saving the day and stopping crime. Yeah, I like the sound of that ... hero ("Kill it! Kill it with fire!" Yeah, that just happened too).
If you aren't a hardcore reader and stick mainly to what I personally would consider a fluff read, then that's all well and good too. This is about putting down a book that you aren't enjoying rather then feeling obligated to finish it. Any reader is a good reader in my opinion. Fluff or no fluff. Whatever gets a person reading can't be entirely a bad thing. But when it comes to personal tastes, ain't nobody got time for dat (that totally just happened).