That Acer Aspire you listed is over $700, not half the price. It's also 25% heavier, has a 5400 rpm HDD instead of SSD, is made of plastic, runs Windows 7, and has crappy Intel integrated graphics. If you don't see the difference then the MBA is definitely not for you.
Enjoy your Acer.
The Acer comes with adequate RAM, unlike the MBA. It's also upgradeable, with a replaceable battery. Without giving up much in form factor, it has a DVD Super Multi Drive, 320 GB of storage, FOUR USB ports, an HDMI port (insanely useful for many of us), a media card reader, and a full 64 bit operating system. It has an aluminum case and sells for about $700 on Amazon.
Certainly the MBA has the Acer beat in some ways, but the Acer beats the MBA in other ways, and at a much more competitive price. Apple should be embarrassed to even offer the MBA in a 2 GB configuration. Most $500 netbooks these days do better.