Cleaning robot industry to grow six-fold in six years (1-23-08)
The worldwide market for cleaning robots is expected to grow from $295 million in 2007 to $1.8 billion in 2014, as indicated by a press release about the Research and Markets report for cleaning robots.

The report includes in its definition of cleaning robots those that perform floor cleaning, lawn mowing, pool cleaning, and home services, the release stated. 

At this point the prices for the robots are fairly high (thousands) and not in a price range for most homes. But as prices drop and the efficiency of the robots increase it could result in a more purchases and a decrease in the sales of self operated vacuums. Full article from Research and Markets