The BookCat program is pretty cool. I'm sure there are similar programs out there, but I've only used this one so I this is the only one I can speak about. It's very easy to enter the information. Just type in the ISBN number and select which sources you want it to check and voila, you now have the author, title, publisher, etc. already entered into the catalogue. I usually have the program check Amazon USA, Amazon UK, Amazon Canada and the Library of Congress. But if you're in the States and most of your books were purchased new, then you probably only need to check Amazon USA.
If the book is too old to have an ISBN number (published before 1970... and even many books published in the early 70's), you might still be able to have the program enter the majority of the information for you if you can find your book in the Library of Congress Online Catalog and it has a Library of Congress catalog number.
Sometimes you might need to tweak some of the information, but it's a very user-friendly computer program so that's not a problem. And it's great for slightly OCD people like me. I have 11 different bookshelves in my apartment and some of them are divided into different sections (for example, Biographies and Social Sciences share one shelving unit). I tend to group my books according to the Dewey decimal system, which makes for easy decision making... very helpful when you have this many books. But once they're grouped I just figure out location according to space and how much I need the books to be near my computer. Anyway, the reason I'm putting my anal-retentive habits on display is to mention that you can easily include location information for each book as you enter it. A feature that I particularly like.
So if you are an avid book collector (and maybe a little OCD), I highly recommend a catalogue program like BookCat.