The Making Of Dwarf Fortress (2008)

Tarn supports himself primarily with donations from Dwarf Fortress enthusiasts.

He's been doing the donation model for years, and it looks like he receives about $3000/month: http://www.bay12forums.com/smf/index.php?topic=87996.0

There was a recent discussion on the New York Times article: The Brilliance of Dwarf Fortress

I really liked the part about water physics simulation.

Agreed.

It's an awesome bit of hackery getting that & all the other systems running in realtime.

Respect, Dwarf Fortress, respect. :)

Are there any other games, text-based MUDs, for example, that approach the level of complexity of DF?

one which springs to mind is nethack, but the game has quite a different nature (much less open-ended).

Not really the same, but Angband is quite well regarded (seeing as how Nethack has already been mentioned).