I look at other search engines such as Yahoo and Bing and think to myself over the last 5 years I have never used them, I always use Google. "Googling" something has become part of normal language, you don't search the Internet you "Google" it. It's just the same as vacuum cleaners are called Hoovers. In a bizarre way Dyson's are seen as the best kind of Hoovers these days!
With the simplicity of Google, the neat features it has gradually added to it like blogs, email, Google Reader etc I just can't see anything replacing Google as the de facto standard for searching the Web.