Today, Google has an ad for its Nexus 7 tablet up on google.com in the US. Between search, a mobile OS, hardware and a social network, Google apparently does absolutely everything now.
Even though the ad is only shown to visitors in the US, it's an obnoxious departure from the comfort and familiarity of a typically sparse page. And it's arguably an unfair advantage for its own product, considering Google doesn't usually advertise other devices in that sacred white space. If you started seeing ads on Google's home page, would it be enough to make you use Bing or another search engine? What's your breaking point?