At the last company I worked at there were several people who regularly visited our other offices in different countries. They only took carry-on bags for speed at the airport. A thinner and lighter laptop like the Air makes a big difference to how much other stuff you can take. One of them had a hideously expensive carbon fibre Sony Vaio for this very reason. A MacBook Air seems positively cheap in comparison.
I agree - while I purchased the new MacBook Pro that just came out, I have a buddy with an Air - he does mundane tasks, but he is constantly switching from apple mail, to internet, to windows outlook mail, to presentation software, to his doc files, to file manager, etc... I don't know about Macs, but on PCs, switching rapidly from window to window to window and doing various work, copy / pasting, etc.. it does not take long to start bogging down due to the I/O - on the Air, it just keeps going, I suspect largely due to the SSD being so fast. So, while many people talk about the overall processing speed for a particular task, I think that a lot of people are doing many small things on a frequent basis, and loading the software, and shutting down, etc takes a lot of time with HD vs SSD... I am planning on replacing my optical drive ffrom the MBP within the first year (hoping the prices of SSD will continue to drop) for just this purpose - use the SSD for programs / computing, and the HD primarily just for storage / databackup.
The lower end 13" "Pro" isn't really a true Pro, IMHO. Lack of discrete GPU makes it simply a Macbook in Macbook Pro clothing. For someone in the market for laptop who is just going to do everyday but work heavy tasks (spreadsheets, word processing, presentations, web surfing, etc.) with a heavy emphasis on multitasking and doing such things on the go, I'd honestly point them to the Air over the lower end Pro as it's a better overall value in that it's much lighter and is zippier on a day to day basis. For someone doing more intensive tasks like heavier photo and movie editing, design work, etc., then I'd point them to the higher end Pros, starting with the 15" Pro if they don't want to spend too much. Heavier, sure, but battery life makes it good for on set usage and while it lacks the SSD, there is an option to swap the HDD with an SSD, and the processors are faster which will be noticeable on graphics intensive tasks. If someone is going to just use it for casual use, websurfing, social network updating, and entertainment related tasks (books, movies, simple games), with a few document and productivity uses here and there, I'd honestly tell them to forget a laptop completely and get an iOS device. It's fast enough, the battery life is pretty damned good, and it's less expensive by far. The only "holes" in Apple's line up, IMHO, are the lower end Macbook "Pro" (the one without the discrete GPU), Mac Mini, and Apple TV. Those are the three products that I just can't recommend to anyone, honestly, as there are better and more affordable options from other vendors that hit the uses typical of those products.
