Design site Nifty Tutorials has posted a practical step by step on how to create a mosaic effect for your photographs using Photoshop. From start to finish, this shouldn't take you more than (tops) 10 minutes, and it really makes a cool looking transformation.

http://lifehacker.com/assets/resources/2007/07/mosaic.png

http://niftytutorials.com/basics/transform-your-photos-into-a-beautiful-mosaic/1/