Well, a long time ago I just did it so much that I lost my drive. But browsing through my old request thread, I see that a lot of people still use the signatures that I made for them 2 years ago, and it's kind of nice. I'm thinking of doing it again.
I've got less free time to do it these days than ever, but it's not like I don't ever have downtime. It's just kind of easy to get burnt out on them if you do too many, but it's really fun and it's gratifying when people like something you make, too.