We use a web based application that provides what did you read, internal reviews, what do we own, what is on our wish list, who's borrowed what etc etc etc.
That exports to an Openoffice.org spreadsheet if I need it to - that way I can run it on all of the desktops and the laptops if they are offline - and directly to a little database application that I run on my Palm.
I started logging everything I read in 1968. Why? Who knows why a teenager does anything? Maybe I just wanted to savor the list. I read 300+ books a year at that time, and tracked them in three other forms of list for a year after, so they stuck in my memory pretty well. Now that they are on the computer, I can search out what I've read by a particular author or find out if I've read a particular title (unless the book has been renamed!) A graph shows me what broad category I've been reading the most of for the past year. If I was reviewing it or editing it, I notate that, too. I also have a Friends and Family Book Blog, a year old now, in which several of us record our reading with brief comments.
I started keeping a record of what I read when I joined email groups and started posting monthly reads. I started adding books I owned but hadn't read when I found myself buying duplicates. My first database, starting around 1995, was an MS Works file. Several years ago I started using Readerware, which has an add-on that syncs with my Palm. I keep my TBF list in an EndNote library, which I can also sync to my Palm. EndNote is reference management software that I get free from work.
I started keeping a record in 2006, but nothing more than the title and author. For this year, I'm reviewing each one. If it's really good I don't say much, because I'll be recommending it to my readership, and I hate spoilters. This year's reviews are on my blog, and I've got all from both years registered with LibraryThing.
I just started doing this in January of this year. I do it purely because I can no longer remember the title and authors of all the books I've read, and writing them down helps. I got tired of bringing home books that began to seem all too familiar a few pages in, whether from the library or from a store where I'd just paid for something that was no longer what I wanted to read. The books I want to re-read, I do keep, and I remember those.
Since I was writing author and title down anyway, I decided to go ahead and do stars to signify how much I liked the book. It's only for my own use, though if somebody asks "What were the best books?" I might consult my new-born list.
I keep very basic records on my computer. I have a fresh file for every year and I just list the name of the author, name of the book and a rating out of five. If I make a written comment it's only a word or two (so that it fits into the column of the table). I've done this for about six years and it helps to remind me of authors that I've really enjoyed and might want to read more of.
I have a nice hardback notebook dh bought me some years ago in which I note, for each month, the titles of the books I read. So I note, the date I finish the book, it's title and author as well as 1 to 5 stars, 5 being a book I loved so much I might have forgotten to eat and sleep ;o) I have noted all the books I've read since 1999 in it, and I love to see what I've read when...
I started keeping track of my reading last December when I started joining online book clubs. So far I've been using word processing to keep my list of title and author and in which month I read it. I haven't done any rating of the books, as I tend to talk about them in detail through my groups. I made a 2007 reading resolution to read at least five books each month, with at least two of them being non-fiction, as I have a big library of unread non-fiction books, and I keep book list handy to make sure I'm meeting my goal.
At the moment I'm working on compiling a list of books that I've bought (read and unread), to keep me from buying the same books by accident. There are 300-400 books in my TBR pile already, but I can't seem to stop acquiring them! :)
For the last three years I've kept track of books in a spreadsheet by author and title, as well as the date I finished reading it. But this thread has inspired me to start listing books on LibraryThing. Seems like a neat idea.