The rumors of a slim Sony PS3 appeared already in early 2008. Around E3 2009 the rumors about the slim PS3 got pretty hot again with leaked shots of packaging and case designs.
If you still had doubts that Sony is going to release a slim Sony PS3, Amazon in Germany can help you. Amazon in Germany has an empty listing for a Sony PlayStation 3 Konsole slim. The listing format follows that of the PS2 slim and is listed under the Sony Computer Entertainment company.
It is the weekend and it is summer holidays in Germany. So basically nobody works. I assume the listing will at least last until Monday and the guys at the Japanese Sony headquarters will go nuts over the weekend trying to reach somebody to delete the entry.

See the listing of the Slim Sony PS3 on Amazon.de; Via Engadget. You can register to get updated when it is available.