I've also got both--a 1.6/120 Rev B. Air and a Loaded CTO 2.8 Late 08 MBP.
To add to the sweetness of the setup I have an ACD as well.
The 15 inch MBP is my desktop replacement but I can still take it somewhere if I really want/need to, and it is connected to the ACD right now (though I'm typing from the Bluetooth wireless keyboard I bought this weekend
)
The Air is my work laptop that I bring with me back and forth. I am a teacher and I teach at two schools, so I needed portability, and I didn't want to subject my beautiful pro to work files nor chalk dust getting inside it. I wanted the pro to remain home pristine, as my master machine.
I bought the Air and absolutely love it. I use both computers every single day; the Air all day at work, and the MBP/ACD at home at night, like right now.
If you get both, you will NOT regret it. Trust me.