Shares in Rightmove, a UK web site for house sales, have dropped  by move then 10% over the last couple of days, following a report by the Financial Times that “Google is in talks with British estate agents to launch an online property portal.”

I do not know what chances of success this venture has. Google does not instantly dominate any market into which it moves; the combination of Google Checkout and Google Shopping hasn’t killed off PayPal/eBay or Amazon as yet.

What interests me though is the impact of the rumour. It is not  only Google’s size and profitability; it is the fact that Google is for many (most?) people the portal to the Web, giving it huge power to reach any Web-based market.

The restraining factor is that it is difficult for Google to exploit that power without falling foul of legislation that protects free markets. When I search for a product on Google, I don’t see any evidence that it favours its own shopping site, for example; though having said that I am only one click away from the Shopping link at the top of the page that searches only Google’s site.

Still, drawing the line between what is and is not reasonable is hard to do. For example, what if Google had a “search for houses on sale here” link in Google Maps?

If Android and later Chrome OS succeed, Google may become the portal to more than just the Web. Its services will have geo-location data as well. Its data-gathering algorithms might learn our shopping and eating out preferences and guide us with uncanny prescience towards things that we enjoy.

I am not surprised that Google rumours have the power to move markets.