o2drink: what symptoms are you experiencing?
For the longest time, I couldn't get ANYTHING to work with the wifi shield. After finally exchanging emails with someone who did get it working, they suggested I try an older Arduino IDE version. Specifically, v1.0.2. And magically, that was the problem.
My set up: Arduino Uno R3, official wifi shield (not sure what revision/firmware, but bought recently). Jumped pin 3 and 7 (or else it shows no shield detected). Using a TPLink portable router. Use IDE v1.0.2, and the sample wifi shield web server code (ie, what you posted), and it all works. If I use a later IDE, it connects to the router, says it is ready for connections, can ping the IP, but doesn't ever serve anything to browser requests.
-borgchick