No idea how many times I've read HHGTTG. Dune I must have read about four or five times. I've read most of Pratchett's books at least three times.
There are many others.
I like to reread.
HHGTTG?
When I was a kid and had access to fewer books, I re-read books more often. Twice was the standard. ...
Exaclty- that's how I was too.
In 6th grade I read 1-40 of Sweet Valley High. Each one at least twice. A few more than that. I also knew where some fave scenes were to reread. After a while they kept intoducing new people instead of developing the characters I already knew. And I was older. So I tapered off. They had Special Editions, too. I would read one now and then through High School, and even in College, they had two SAGA's, the maternal family tree and the parternal family tree. They're easy reads, and I enjoyed them. I can tell you the continuity errors. Like some of the special additions (set in the summer) were written before some of the series and so one of the girls had the wrong boyfirend, etc. Way more info than you wanted, isn't it?
I also accidently stole a library book, we moved and I didn't know it got packed with my stuff. It was book one of another teen series called Crystal Falls. From 6th grade thru college I read it over ten times. Comfort food. I wasn't moved though, to read the rest of the series until after several readings, but couldn't find it. (Before amazon.) Now I don't really care.
What do you guys get out of re-reading? I notice details I missed the first time. There is the comfort aspect for some of them. BUt I noticed with the Crystal Falls book- on the first readings, I pictured the characters by my initial impression, my first inkling of appearance, and after the 8th reading I think, i started picturing them as they were described. FOr instance, the popular girl, Chelsea, was described as having short hair 'against the trend' but the popular trendy girls at my school had short hair, so when I read 'against the trend' I pictured LONG hair, and her friend Perky- as having short hair. Also Dawn the main character I pictured with short hair. But after the 8th reading, I started seeing them as descirbed, with proper hair length. I find that interesting, like my brain finally reconciled everything on the page.
I have trouble with my own description in fiction. I get right to the action and dialogue and forget to tell the reader what my character looks like. I wonder if that is part of it. I tend to just picture characters on my own without worrying about description, obviously I take it into account, like the blonde is blonde, you know. I don't even know where to insert description sometimes. Is that because as a reader I don't worry to much about it unless it matters to the story? hmmmm? I'm thinking out loud (er while typing) here.
When I was finally given a set of my own as a present from my parents, I proceeded to re-read them as often as I could. It is likely that I have read each one 40 or 50 times over the years. 
