When I got it, I did go through my DMG reading each and every little bit. While I didn't retain a lot of the random charts and information, I did get a lot of useful bookmarks in there for future reference. I have gone through some sections the PHB a lot, but I have gone through the whole thing at least once.
Otherwise, I have flipped through the whole MM, but I see no need to read each and every creature. I usually pull out a fun and fitting monster, like a snowball throwing yeti atop a snowy mountain, and read the creature's stats as the battle starts. Other times I'll pick a random CR that is about right and fluff it into the monster I want. Either way, I use the MM as a reference and not something I need to know. Plus, that makes it much more exciting when I'm a PC and I have no idea what the monster's capabilities are or how deadly it may be.