Like making blinky light projects, but not able to pump enough performance out of those measly 8 bit instructions on your Arduino? Yeah, us too! Thankfully, the folks over at liquidware antipasto have us covered with this liquid-cooled, overclocked Arduino.
All joking aside, it can be a fun experiment to try overclocking a microcontroller (skip the liquid cooling part, though). If you are actually running into the limits of performance that you can squeeze out of the Arduino platform, you might want to consider a faster system, such as the Maple.