I stumbled upon a very interesting question at Yahoo Answers and, surprisingly, the answers were quite thought-provoking. The question was: "What is the difference between Yahoo and Google?" and here are some of my favorite answers (slightly edited):
ThisNickIsTaken: "Google has a philosophy of keeping things simple so that people who are technically challenged can use it without getting confused, Also that simple things are fast.. Yahoo believes in feature rich application.. their products are more customizable and complex."
Gags: "It's a difficult one to answer since both companies are positioned very very differently; on face value, Yahoo looks hip and colorful, whereas Google looks simple and elegant; (...) Google is more thoughtful and strategic, Yahoo is flamboyant and more reactive; Google concentrates on value added solutions rather than presentation and Yahoo concentrates on superb presentation followed by value creation."
Ravelin101: "Yahoo has tons of media and ADS (loads slower). Google search is better (faster) only text ads. I started with Yahoo since I've known it first: Mail, Photos (now Flickr), Geocities but since Google's introduction, I've been moving things to Google Mail, Photos (Picasa), Googlepages."
So Google is strongly associated with simplicity, usefulness, pages that load fast (in one word: text), while Yahoo is connected with rich interfaces, complex designs, pages that load slowly (in one word: multimedia). Gags even called Yahoo flamboyant, which means "elaborately and heavily ornamented". It will be interesting to see if the acquisitions of YouTube and DoubleClick will change people's perception about Google.
Defining Google collaboratively