I'm a hardcore re-reader and re-watcher and 99.9% of the time order exactly the same thing at restaurants and coffee shops and ice-cream parlors because I like repeating fantastic experiences. Well-loved books and movies (and sandwiches) are like old friends. You can always count on them to look and feel (and taste) the same, to move you in the same ways.
I've been re-reading Megan Whalen Turner's Attolia series over the last week or so, and while, admittedly, nothing is quite like the first time through, with all those wonderful startling revelations and aha! moments, I still very, very much enjoyed them. In fact they were still eliciting audible reactions from me, to the point where my roommate looked up from her important doctoral studies to remark, "You do realize you've read that before." :-)
Another reason I re-read is that if I don't read a book at least twice, details tend to fade, and I'm left only with vague impressions of I liked it or didn't like it, which isn't ultimately very useful. And some books stand up to multiple readings more than others; some I find kind of "meh" on a second read, some I find as amazing as I remembered, and some—like, for example, the Attolia series—you almost have to read more than once to soak up all the awesome and intricate things that are going on.
And then there's mood to consider. As much as I love them, sometimes I'm simply not in the mood to adventure into a brand new book and unknown territory. There's a certain amount of comfort in knowing exactly what's coming and looking forward to parts I already have completely memorized and revisiting beloved characters and just experiencing the story again.
Man, now I want to go re-read Lord of the Rings. It's been a few years…
What about you? Are you a habitual re-reader?