Even after the release of Windows 7, it looks like Microsoft won't be quick to ditch Vista according to Computer World. Microsoft plans to continue selling Vista until January 2011. However, they will drop support for Vista in less than 3 years.
This seems to go against an earlier hint by a Microsoft General Manager that the company would get rid of Vista as soon as Windows 7 was released.
However, Microsoft not ditching Vista as soon as Windows 7 is released shouldn't come as a surprise. It's a company policy to keep an OS in distribution for 4 years after its debut.