As of Minecraft beta 1.3, you can now put in a "map seed" when making a new level.
What this means is, the level will be specifically fit to that string of text/numbers (But not correlated in any way).
What you all do is,
1. Start a new game in Minecraft
2. For the seed, put in your forum name
3. Explore, and post interesting screenshots
gamefreak:
Was a cave just about 10 blocks down.