I right click and clear the window, but when i reload the app or get another message all my old stuff comes back, and its quite laggy with all the pics I have sent back and forth with my wife. Am I just overlooking this or is there bug?
Happens to me too... Try this: Messages > Preferences > Messages > Delete all History when conversation are closed
Messages > Preferences > Messages > Delete all History ^ that works... I just didn't close the conversation, I thought it meant to quit Message. But "clear transcript" via right click is glitchy.
That is because it appears only on the Messages that comes with Mountain Lion. Of course, this is the ML forum so really you shouldn't be surprised
I have mountain lion and don't have the option to delete the cache either. To get round this: At the desktop, hold option while you click the Go menu, and select the Library. Within the Library, drag the Messages folder to the Trash. While you're in the Library, you could reclaim some wasted space if you like. Quit all open applications, then delete the Cache folder, and within the iTunes folder you could delete all those iPhone/iPad/iPod software updates. Now restart.