I don't. I just don't give a shit. I like writing new things, but I could not care less about keeping them going once I've created them.
Here's what happens. My Towelie library has a fork with a new name, rewritten with a different parser. My Utility Belt gem has a fork with a new name, rewritten for Ruby 1.9. My password gem has a fork with a new name, rewritten with different password generation rules. If your software is good enough for people to use, but you don't maintain it, they'll maintain it for you. You lose ownership, but if you want ownership, just maintain your code.
This is why distributed version control is great. Compare this to the ceremony, process, and fear associated with forking projects in the Subversion world. Using modern tools means you're free to give away good code any time you come up with it, and you don't need to be burdened by its maintenance, unless you want to be.