What is considered a "normal" personal computer will reach a tipping point in around February 2008. The norm will become low power Linux computers using the Internet for data storage.
The normal computer bought for home or business in 2007 has a DVD drive, multi-hundred gigabyte hard disk, Microsoft Windows and multi-hundred Watt power supply and costs around $1,000. If you buy a $500 low power Linux computer, like the Zonbu or Asus Eee PC, which runs Linux, uses tens of watts and depends on the Internet for storage, you will be considered a bit odd; perhaps a greenie, academic or an anarchist.
However, this may change soon and quite suddenly. By the end of 2008 I expect that the idea that you might spend thousands of dollars on a computer and propose to store data on it long term will be considered more than just odd. To consume hundreds of Watts of power to do so will be considered anti-social. Propose spending hundreds of dollars on operating system and basic office software licenses at at a company and you will be sacked, try it in a government agency and you will be charged with corruption.
The normal PC will have a processor equivalent to a 1.5GHz VIA C7-M or 900MHz Intel Celeron-M ULV 353, 512MB RAM and either 4 2 GB of flash disk or a 60GB hard disk. Most PCs will not have a DVD or CD ROM. There will be minimal hardware support for graphics and the computer will use less than 20 Watts of power. These computers will cost less than $500, some as low as $200.
If this sounds far fetched, consider the change which happened with the Internet and the web in the mid 1990s: this went from being an academic experiment to the mainstream. The change with PCs can happen much quicker, as it has the Internet and web to provide the infrastructure, support and the marketing of the idea.