Evernote SDK 3.0 includes many improvements and changes.
A new build target has been added to the project to allow building a dynamically linked iOS framework
Generics and nullability annotations have been added to much of the UI, and many methods have been renamed for Swift
Many methods have been renamed to comply more closely to Cocoa naming conventions.
The sample projects have been moved to their own Xcode files, and a Swift sample has been added.
The EDAM API has been updated to support newer features in the Evernote API
Issues with using the Evernote SDK with CocoaPods have been fixed
Unfortunately part of the changes have meant that progress blocks are no longer supported in the latest SDK.
For the most part your code should still work when upgrading from the 2.0 version of the framework in Objective-C. However, many methods have been deprecated which will produce warnings. It is recommended you upgrade these to the replacement methods as soon as possible, as the deprecated versions may be removed in a future release.
If you are using Swift, you may have more work to do. The deprecated methods are not exposed to Swift, and several APIs have been renamed for Swift to better reflect the API naming guidelines in Swift 3.0.