Userscript are a great way to add functionality to your browser. And many people have Greasemonkey installed. But if you want to reach people without GM installed with your script, you need to wrap it up as a real, native, full-blown Browser Add-On, for example a Firefox extension, an .xpi file.
The BabelExt framework, once fully working, will be a great way to do cross-browser add-on development. And a few years ago, for Firefox, the online script compiler also was an easy way of quickly bundling your GM script as a browser extension. Was, because it's mainly outdated.
It's up-to-date, it simply works, and a very thin wrapper around your JS code. And with it, it's easy to develop, maintain, update and bundle your script. If you're a Greasemonkey developer, and recently fed up with Userscript.org being down, simply bundling your script may be a great solution. Try it!