I was scared away from purchasing a MacBook Pro with a Mini-Display Port just because of all the reviews on Apple.com saying how that converter was horrible. I'm happy I did, because it caused me to wait for a MacBook Air 13", and not only did I get a computer that is better for me (I really don't need all the features and power of the latest and greatest MBP) - They also seemed to have fixed the problems with the converter. I spend 10-12 hours a day with my MBAir 13" 1440x900and my Dell 2560x1600.
The Converter works fine, I _love_ the mini-display port form factor, Happy to hear they are adapting it for thunderbolt, (Interesting to see the similarity in Bus Naming "FIRE WIRE" "THUNDER BOLT") - Only downside is that it requires a USB port to power it, but, on the pro side, the MBAir comes with two!