I used to love Mac Mail. It was simple and relatively fast. And when I started working at an office where everything was on Exchange server, it was a nice alternative to Outlook.
But Mountain Lion (10.8) ruined everything. I don't know what they did to Mac Mail but its the buggiest piece of software on all of Mac OS at the moment. It's frequently unresponsive to GUI interaction (click reply and nothing happens), it doesn't show email messages ("this message has no content"), or it simply locks up. In all situations I have to quit and restart it to get it back.
I want the old Mac Mail :-(