David Sparks and Brett Terpstra have written a great book called 60 Mountain Lion Tips, and I can't recommend it enough. I've already been through the whole book, and my copy is now full of highlights and bookmarks that I can't wait to implement.
"60 tips" is a bit misleading. It's more like 60 topics because virtually every tip topic is accompanied by a concise, but information-rich screencast. Many of the videos are loaded with extra tricks, advice, and demonstrations.
Everyone that reads this book will learn something new about the latest Mac operating system, Mountain Lion. If just one of the tips makes a recurring task easier, then the book, priced only at $7, has already paid you back.