Many of us here at Invo have been using the Arduino quite a bit. From making claws for costumes to retail environment behavior to coffee electronics – it is incredible what you can do with these microcontrollers. However, there still is not a straightforward way of getting data out of your Arduino, onto the internet and accessible via a web app.
The personal project I've been working on has been tracking physical activity not covered by pedometers (vague, I know) and then having a web app to display that historical data. Coming from a design background with a light technical bend (some C++ and ActionScript) I am in familiar territory... but its been a while.