I finally upgraded my 2008 MacBook Aluminum! I was originally going to purchase the 13" MacBook Air (MBA) but ended up leaving Bestbuy with the 13" MacBook Pro w/Retina display. It's only 0.5 lbs heavier than the Air and is just slightly thicker. Surprisingly though it has a smaller footprint than the MBA.
Really though, it's all about getting in on that Retinal display. For $200 more than the MacBook Air, you can get the 13" MacBook Pro w/Retina that is almost as thin/light, has 9+ hours battery life, and a more powerful cpu/gpu not to mention a full HDMI port and dual Thunderbolt 2 ports.
To me, a laptop screen is so important. It is, after all, how you interact with the device. It made sense for me to spend a little extra and give up some portability for a more powerful laptop with a much better screen! That being said, the MacBook Air is the perfect laptop if you care mostly about weight and battery life.