I've read most of the books from previous games, but I re-read most of them, and all the new books (though it depends on the character). My current character has a full library in Proudspire, and a fair collection elsewhere.
The scary thing is that I have the shelves mostly sorted by subject matter, so all Dwemer books go in a particular shelf, for example.
its a BIG relief knowing im not the only obsessive one lol, i think a few of you guys are the same as me, but even i couldnt read every book from every game, surely it would take years. lolol, respect to the guys that do, i think my neck would hurt, it starts to ache wen i concentrate too hard lol, damn neck