Minecraft level design test-rig?

Swapping discs in and out over the weekend left me time to mess more with Minecraft and carve out the main chunk of my 'spiral tower'. As I extended out the catacombs it dawned on me that this wouldn't be that bad as a deathmatch map. Not great, but not bad.

Now the PC versions of a lot of shooter games (and also sandbox games) come with level designers, but some are easier to use than others. I wonder if any one else has considered using Minecraft as a test-rig?

It's very simple to use; it runs pretty much anywhere so creating a level, running a server and allowing testers to run around and shoot each other is easy. Even in single player watching someone get lost or not know where to go next allows fine-tuning; then how simple to carve out the basic layout in the actual level designer for a game.

Sure Minecraft has limitations in that everything is a one-unit cube with no curves, but I wonder how much time could be saved using it for at least a first approximation?