I was finally able to buy a 13 inch 2.13Ghz 4MB MBA at the OKC Apple Store this morning but it wasn't easy. I called them on Monday or Tuesday and was told that they would not be stocking any of the 4GB models. I called again yesterday and was told they had the 13 inch 2.13Ghz 4GB in stock. When I got to the store, though, after waiting about 20 minutes to be helped, the kid who went to get it came back shortly and said they didn't have it in stock after all. Woops!
I called the Apple Store again today because I had not got the same answer in 2 tries so maybe there was something new. This time I talked to the guy who is the store's products manager, who as it happens has sold me my iPad. He went and got what I wanted and put my name on the box. When I showed up about 15 minutes later, he met me at the Genius Bar with my MBA in hand.
There was really no decision for me to make between a 2GB and 4GB model because I plan to run Windows 7 under VMware Fusion in Unity mode so that I can multitask running both Windows apps and OS X apps. I just hope that 4GB will be enough, although with the speed of the MBA's flash storage, I am confident that I will be just fine. Will report on that later.