I played most the weekend too. The island I spawned on in my new 1.0 world has proven quite full of things to explore beneath it.
This is my island:
This is my farm so far:
There is a huge hole under the island, goes practically from the surface to the lava layer:
And the hole leads into a huge ravine that seems to run along under the length of the island:
This seed so far has been fun to explore and spelunk in. Although I've come to a startling revelation: there are no sheep on my island. None at all. Lots of pigs, cows, and chickens, but zero sheep. I guess I must travel to find wool...