I agree with Sean. I upgraded to Mountain Lion this morning and have just gotten around to playing with it now. As my screen name suggests, I use a lot of Apple products and the enhancements of ML really make everything work together effortlessly.
I am in school finishing up my Master's degree and having been doing a lot of digital marketing/social media freelance work. The addition of Notes and Reminders for Mac, for me, is amazing. I had a quick meeting this afternoon and created a list of to do items that the client needed done. When I got home and sat down at the computer, my entire to do list was waiting for me.
I feel like this update was all about polish and finesse. There is nothing really earth shattering about Mountain Lion, but all this subtle improvements really make for an outstanding overall package!