Just one, as I rarely use it on anything but obsidian.^ I'm just impressed at the time it must have taken. Not to mention how many diamond picks you went through.
Yep. I poored water on a large lava lake that I had found down in my mine.Or did you use the old lava/water method?
When that was mined out, I built one of those obsidian generators, that turn redstone into obsidian without wasting the lava source block in the process.