2008 MacBook Pro or 2010 MacBook Air
 

Pretty much these are the options for a buddy of mine. Wants a Mac, buying used & these are in the price range he's looking for.

I'm not too sure on advice for Mac's or CPU's, so I'll post the specs here and see what y'all think.

MacBook Pro
Memory: 8 GB
Processor Speed: 2.40 GHz
Operating System: Mac OS X 10.8
Hard Drive Capacity: 250 GB
Release Year: 2008
Screen Size: 13.3"
Processor Type: Intel Core 2 Duo

MacBook Air
Operating System: Mac OS X 10.6, Snow Leopard
Release Year: 2010
Memory: 2 GB
Screen Size: 11.6"
Processor Type: Intel Core 2 Duo
Hard Drive Capacity: 128 GB
Processor Speed: 1.4 GHz

What is he going to be using it for?

I would go with the MacBook Pro. No contest. Unless ultra portability is the most desirable aspect, go with the Pro.

The Air is lacking in space and connections. It's overpriced by the widest margin of Apple devices, and it's only redeeming feature is the size and portability.

Surf the web and watch movies predominately. He's using it for travel.

For travel and web surfing -- Macbook Air would be a good choice (it doesn't have an optical drive!!!!)
Personally, I'd go with the macbook pro...

that's what I told him