Followup.
Not your exact question, but the important point is that overall, the MBAs feel much faster than a MBP. I have a 2009 mid year 13" MBP and the MBA smokes it. A more realistic question would be, how long does it take to do a compile or go through an edit to debug cycle. Thats more of a benchmark.
Its interesting comparing to the MBP. The MBP is able to perform the build faster, but the SSD is so much faster than factoring in load times for various components, the MBA still ended up beating the MBP on the edit to debug cycle. And thats a 1.6ghz 11" w 4GB.
For almost every task I ran on the MBA, it performed faster than the MBP. Again purely because disk access times are so much faster.
The only time I've seen the MBA be notably slower is doing Handbrake compression where it took almost twice as long as my MBP. Not sure why so much slower. Thats more than the CPU speed difference.
The other important place where I've seen the CPU speed have a detrimental effect is in real time processing, such as video playback. The MBAs have trouble playing highdef video which is being processed by the CPU. If the GPU does it, it does great. But if the CPU is involved, it will likely be choppy at best or may not play at all. Generally, if Quicktime plays it, it does better than VLC. Silverlight does better in Safari than Chrome for some reason.
Overall a very fast powerful tiny machine.
My concern and continued debate is if the 11" screen is too small, or too much of a compromise vs. my 13" MBP screen. For some reason the 11" seemed to give me some eye strain. The 13" MBA does not even though its pretty much the same font size. The 11" screen is notably less tall, because of the smaller screen and wider screen aspect ratio.
I keep wondering if the 11" screen may be more difficult to work with when doing UI layouts with interface builder. In particular, laying out an iPad app screen is a challenge because an iPad window has significantly more vertical resolution than is available on the 11" within IB.
I also wonder if running Photoshop or Illustrator or GIMP if it may become tedious to manage the smaller screen.
Bottom line for me, I'm very impressed with the 11" in particular. It is clearly a compromise. The CPU isn't as capable as that of the MBP. So its a grey area debate. Is the much greater portability worth the sacrifice in screen size and CPU speed. You can always buy an SSD to add to the MBP.