People are curious to know if Google Earth shows live images, if Google Checkout is safe. They also wonder if Google is a number, a god or if it's down. Other popular questions: "is Google Toolbar/Google Desktop spyware?", "is Google Maps free?".
Yahoo's questions are mostly related to Yahoo Mail and Yahoo Messenger and most people want to confirm that some Yahoo applications are down.
Google's visitors seem to ask little about Microsoft. The top question: "Is Microsoft Vista good?". They also question if Microsoft is evil, down or a monopoly.