Can you pay the difference and get the 17"? Seems like the best option. Otherwise, MBA is a fantastic machine, but screen real-estate is lacking vs. your 17...
Posting from my iPhone and apologize for grammar and structure and any repitition
So here's the deal. I just picked up my trusty workhorse. They've replaced the keyboard, video display panel, logic board, top case, bottom case, display bezel, both fans and the airport extreme card. I practically have a new machine here!
I also spent 3 hours drawing attention from security for walking around with MY machine comparing it to every laptop on display LOL
For any of you with a non umibody MBP, the new ones are cool but the screens are way way more reflective than ours. Mines glossy FYI.
The 15" is out of running. Too little offered over the 13 and not really any more portable than my 17.
The MBA is nice but I could see the lines clearly and need more HD space. I work in a jungle and watch movies on pirated DVDs. By the time I take a SuperDrive and an external, the portability is moot.
I replicated my workflow on all 4 machines and for my traveling and writing needs, I could get used to the lower screen real estate .. As a second computer.
I've decided to skip the gift offer, I don't want to part with my old classic, overhauled and better looking (I luke the all silver look) MBP. plus, I've got sentimental reasons. What can I say? I'm a collector.
I'm going to keep my rocking machine. Instead of replacing it or giving it away. And paying the difference, I'll spend the difference on a 13 inch for the road. Ill relegate the big boy to a home desktop for the wife or a future media server.
May not be the most logical choice but it makes me happy

my 17 has been around the world with me and I have a lot of memories. I'll keep it around. Wierd to feel this way about a computer but it's been with me during some life changing events and I'm attached to it and don't want to part with it.
I'm going to pick up the base 13", upgrade the HD to 250g for 50 bucks, put that in my old workhorse and buy a 7200 500G drive for the little guy.
Again, this is from my iPhone and may not be the most readable post
eV