The oldest article we found about the Playstation 3 is dated from 1999. The Register featured a story talking about Sony's Processor strategy. In there it says that Sony expects to release the Playstation 3 in 2002. In a story on The Inquirer from April 2003 the possibility of a delay of the Playstation to 2007 was stated.
I think nobody actually knows including Sony when the Playstation 3 will hit the market.

What is known about the Specification of the Playstation 3 is also rather sparse.
In 2002 a story went around that the Playstation 3 is all about Grid computing and is working with IBM to achieve 1,000 fold performance increaese compared the Playstation 2. See ZDNet article.
In January 2003 a patent was discovered that looks like it describes the architecture of the Playstation 3. See this story on The Inquirer. The Latest news is that the PS3 will have facial recognition built-in see the Story on DesignTechnica from last week.

Besides that there are already tons of Web sites dedicated the Sony Playstation 3 reporting mostly about fake Playstation 3 photos and rumors, as hard news are just not available. See the photo on the left that just surfaced. Found at Playstation 3 Resource Center.

The next big thing from Sony is the PSP Handheld Game Console, and currently Sony roles out the PSX Console in Japan. Will see what the Sony Future brings when it arrives.

See Also:
Sony Playstation 2 40GB Add-On Hard Drive Announced
Revolutionary Sony Playstation EyeToy
Top Selling Playstation Games