I thought I might be able to add to this discussion a bit.
I've got a MacBook Pro (Late 2009), 13.3", 2.26GHz C2D. I've replaced the optical drive in it with a 40GB OWC Mercury Extreme Pro SSD which I use as a boot/apps volume. I've also got a new MacBook Air, 11.6", 1.4GHz C2D. The bone-stock $999 model. I bought it because I travel a fair bit and wanted something between my iPad and my MacBook Pros. Even the 13.3" MBP feels like a behemoth when you otherwise make it a point to pack light.
Anyway, the MBP is fast. Not the fastest MBP, but with the SSD, it is incredibly responsive. I've uploaded a few YouTube videos to demonstrate how quickly it boots and launches apps.
http://www.youtube.com/watch?v=EjnBLKH2Mes - Boot from disk chooser screen and launch Quicksilver, Word, PowerPoint, Excel and iTunes.
http://www.youtube.com/watch?v=g4R9tyBp9a0 - Power-on to usable desktop with Chrome auto-launched.
http://www.youtube.com/watch?v=9zUQzGHlYq8 - Boot from disk chooser screen and then manually launch Chrome and Safari.
I thought it would be interesting to see just how quick the MacBook Air was when compared to my MacBook Pro. I expected the MBP to run circles around the Air, but that's not exactly what happened.
http://www.youtube.com/watch?v=ZizRmnexDxA - MacBook Air and MacBook Pro booting simultaneously and launching Quicksilver, Word, PowerPoint and Excel.
I've also run the Xbench Disk tests on both SSDs. Both were run on a cleanly booted system with no other apps (besides Quicksilver) running. You can see the results here:
MacBook Air and
MacBook Pro.
All in all, I am very happy with the performance of the MacBook Air. I'm not using it for Handbrake encodes (that's what the Mac Pro is for), but for web browsing, YouTube, word processing, spreadsheets and coding - basically, every day typical end-user tasks - it's very responsive and fast feeling.
I'm happy to answer questions, run more benchmarks or record more videos. If there's an app that's freely available and you want to see how it launches on the base 11.6" MacBook Air, let me know and I'll post a video for you.