2.0 Ghz processor is recommended for Mac OS X Lion, I think I read that in the App-Store. Its a little sluggish at times Dougal compared to Snow Leopard, so yes there are performance issues. I expect they will be addressed in future patches which is often the case with many OS Updates.
Overall not a lot has changed contrary to what they tell you and thats kinda of reflected in the price.
Most of the changes are in the interface, I can tell you the new interface is really boring and grey. Its like a step backwards and a little forwards at the same time.
Full-screen applications are simply that, as soon as you alt-tab to another application the menu bar and dock re-appear. It effects that application only and is nothing like a public screen experience.
I felt Snow Leopard was perfection anyway now they are just pissing around.
This Lion has more of a mieow and is definitely not king of the jungle just yet.
My Config: Mac Mini (2010), 2.26 Ghz Intel Core 2 Duo, 2GB Ram.