I have an older Pro, a new Air and a new Pro with Retina.
The Pro is great for processing any intense applications. I use it for photo editing, video editing, gaming (not a huge gamer but I like to play once in a while), watching bluray movies, etc.
The Air is great for web browsing, writing papers (Microsoft Office), and any other basic things. For such a small machine, it's really fast thanks to the SSD. I love the portability too. It's so small, it literally takes up no space in my book bag.
The Pro with Retina is the best of both worlds. Thin, fast processor, lots of memory, SSD and it has an amazing screen.
Not putting miles on your Ferrari is like not f*cking your girlfriend so she'll be more desirable to her next boyfriend.