To be honest, my nephew has a MacBook Pro and when I compare it's speed vs mine Air, my Air is much faster.
We both got the base 13'' 2011 model. Only difference is, his model is indeed clocked at 2,3 ghz with a i5 and mine is at 1,7 ghz i5. We both have 4 gb of ram. But mine does have a SSD. And with all basic tasks, my Air performs much better.
Maybe the 2,3 ghz would help with rendering a video for example. But other than that, I see no advantages to a Pro with similar specs.
But we were talking about usb and peripherals, and it seems, the Pro is nothing more "Pro'' at that departement.
I only wish I had chosen the 8 gb ram option when purchasing. Because now, I'm stuck at 4gb. Which is ok, but sometimes especially when I use Final Cut, I wish it had a bit more power to work with.
Other than that, don't think low of the Air, it's really just a better looking Pro.