CSS 3 only clock with multi-touch support.
While playing with various mobile (touch-enabled) OS I noticed that all were using the very same widget for setting the time.
Here is the one used in iOS: http://experiments.warpdesign.fr/WarpClock/img/ios_time_settings.jpg
... and the one used in the latest Android (ICS): http://experiments.warpdesign.fr/WarpClock/img/ics_time_settings.jpg
They both share the same usage: you have to scroll to choose your number. The problem is that it may take some time before reaching the correct number. Not to mention you may go too fast and skip it.
How about having a true analog clock and being able to move the clock hand ?
Here is a little clock widget in which you may use directly move the hand to set the time.
Just for the fun this is made of CSS only so it can easily scale across different devices. This should work with any touch-enabled devices as well as traditional mouse-driven devices. Microsoft-specific touch events aren't supported right now.