I spend 8-14 hours a day on domaining, if I'm not out fixing client's computers. I have almost shut down my former computer support business now, in favor of domaining and I love it.
When I go to bed, I use my iPhone/HTC to check my e-mail and also browse for domains to purchase. I also wake up a lot in the middle of the night to catch a last-minute auction, or to reply to a PM/e-mail.
Yes. . My girlfriend gets a bit tired of it sometimes.. But I consider it my job now and she supports me all the way.