What are you talking about? Their CEO, Phil Libin, has promised they were working on precisely this (notebook-level encryption), and planned to release it before the end of the year or shortly afterwards. From the Evernote Podcast episode 40, from October 30th, around 51 minutes in: "We actually got a super cool, uh, we're really really beefing up how we do client-side encryption across the board […] it's something we are hard at work now across multiple clients."