I read about it in PC Gamer probably a year or so ago, and thought "that looks cool", but was playing GalCiv2 at the time so didn't look into it.
Then I saw another reference to it on one of the independent gaming sites (around the time that I'd grown totally jaded with all commercial & mainstream game offerings). The dude who referenced it on the site obviously was having immense fun with the game, so I took a much closer look at DF.. since then DF has been the only game I've played.
I've been playing computer games since the age of 4, starting in 1984, and the only game that still gives that old school feeling of fun is DF; but I've drifted away from gaming quite a bit in the last couple of years, played everything there is to play. The fact that DF can hold the rapt attention of even as jaded an old-time gamer as me is a testament to its genius.
The thing I love most about DF is that you can make of your game whatever you want it to be, you've got the tools to create and carve out something that's your own on each map that you play.. there really isn't any other game that even remotely has this creative aspect of such depth to it. So DF keeps me hooked.
It's amazing how much a game can accomplish by simply letting the gamer have room to use his/her imagination. I think that this is what old school Apple/Commodore games had going for them, and my fondest memories are from games that had this element to them.
Anyway, long post, but long live DF.