Serenity Caldwell, writing for Macworld:

… Lion is coming. To prepare us for the changes ahead, Apple has posted a big summary on its website listing all of the more than 250 new features present in this version of OS X—but let’s be reasonable: As excited as you might be, you don’t have time to read up on every single one. Instead, let us do the work for you, and highlight some of the coolest new tricks your Mac will be able to turn in Lion. Go read over the 5 obscure features Serenity has written about. I think she did a good job at picking 5 crucial features not covered in the presentation from WWDC. I've seen and used all 5 of these in the developer preview I'm running and can attest to how well they work.