So while finding Obsidian since everyone wants it, I found a way to get endless water flowing (which, note, can be annoying and potentially lethal if it doesn't flow somewhere).

This stream of water does not stop. I started to drain a large pool and then went down so the surface was off-screen and continued to mine some obsidian. The water has not since stopped and continues to flow (over lava for more obsidian, yay), and it's rerouted to flow off of the edge somewhere into some pit where I can't see the bottom so it must not actually collect anywhere. I'm guessing I'll end up dying somehow since if I hit a dead end I'll drown.
But yeah.
Anybody want some Obsidian? I can get you some eventually.
I want to do a dungeon, Messes. :D