In general, I'm more than pleased with the changes in Mountain Lion, but in any release there are a few niggling things that bug me. One of them involves the behavior of the Messages app which replaces iChat. When you give focus to the app by clicking on its icon in the Dock, it opens the unified Messages window even if it's closed if you don't have other windows (like the Buddy List) open. I'm not a fan of the behavior, and was wondering if there's any way to change it.
Also, as a bit of a twofer, when you double click a contact in the Buddy List, it opens the chat in the unified Messages window, instead of its own separate window. If that behavior could be changed as well, it would be totally sweet.