Things broken in Lion for me - 1) Flash is broken very badly in Google Chrome. Slightly lesser broken in Firefox. 2) Resizing a video playing window will show artifacts. 3) There is a lag in the desktop showing up after credentials are entered into the login screen. 4) A small number of apps appear to start automatically on bootup. I dont know if Leopard is trying to remember what I was running before I shutdown.

All things being said none of them is a major issue. Then again I was a Vista user back in the day and I was just as satisfied with it. My only nitpick with Vista was that copying directories with lot of small files was very slow.