I have to say that the 11.6" is an awesome little machine, and that's just from playing with it for 45 minutes in the Apple Store this afternoon (I only got my hands on the 1.4 GHz 64GB).
For day to day tasks, I don't see how it couldn't be more than adequate; it was certainly faster than my 2.4 GHz 20" mid-2007 iMac. People who are worrying about the processor need not worry, we've all just been brainwashed by Intel's marketing. Remember the days when a 500MHz PPC could run circles around a 2.0 GHz Wintel machine? It's a similar theory here, the SSD makes up for the lower clock speed.
As for the screen, it's beautiful. With the high resolution, there's no need to worry IMO. You have a little bit more screen real-estate than you would get on a 13" MBP. There's also the fact that it can drive a 27" Cinema Display at full resolution (2560 x 1440); which is the perfect solution for doing anything that requires more real-estate.
I agree with what everyone has said in regards to the weight of the MBA vs. the MBP. Just from holding them off the tables in the stores, I was able to tell how much of a difference a little bit of weight makes. The MBP gets heavy after 30 seconds in your hand, but the Air is litterally like Air, you could almost forget that it is in your hand (I would have except it almost got knocked out of my hand by some d-bag in the store who had an ego and an attitude bigger than SJ^1,000,000).
-Don