First, they put the sync and account management features under one tab called “Sync” so you can sync when you want to sync. On top of that, it’s now possible to search and sync at the same time. That’s a tremendous convenience boost.
But since you can’t always rely on sync, they’ve also vastly expanded the local cache capabilities. Notes created on your iPhone or iPod touch are automatically cached locally. Furthermore, Premium users can now cache entire notebooks. This is in addition to using Favorites for storing individual notes. That’s all tied together with the new ability to search local notes. Should be a huge help when you’re without a signal, or if you use an iPod touch and rely entirely on wifi.
There are several other improvements, such as doubling the audio note time, options for editing rich text notes, support for additional languages, and increased speed. Full details from the Evernote Blogcast.