I don't know how I missed this thread earlier, especially when I had the "do you re-read books" poll going. Anyway, yes, I re-read, and so do about half the members of MobileRead, based on the poll. I re-read for all the reasons mentioned above-- because of the comfort of familiarity, to get more out of each reading, to admire the author's use of language, to re-experience a certain feeling, etc.
Also, as I'm getting older, I've found that if I wait a while before re-reading, I've often forgotten many of the twists and turns. I may remember the overall outcome, but not how we get there, which (in a good book) is much of the fun.
And as time goes by, the amount of time I have to wait seems to be getting shorter!