The last long film I sat through was Magnolia and that was 3 hours 8 minutes...and it seemed like an eternity. I have a feeling I'll be savoring every minute of this film, though, hoping it won't end. Magnolia was a bit long in the tooth, but after reading Fellowship a few times, you really do need 3 hours to flesh out the story.
No intermission from what I know, so no beverages unless you have a well-trained bladder.