I'm interested in how other people develop themes and plugins for WordPress. To me, the in-browser editor in the admin panel just doesn't cut it. Currently, I'm just using an IDE with a PHP plugin (NetBeans), pulling down my development web directory from my server, editing in there, pushing up to test, and then migrating over to live.
I'm looking for how other people use their tools of choice to manage workflows for developing, testing, and deploying themes, plugins, and testing the latest versions of WordPress against these before going live.
I've made this a community wiki so that other people can share there development process. I'm not expecting to find a singular right answer here - your process is your own, and I wouldn't expect what you do to just work for myself or anyone else. I'm just interested in improving my ability to develop plugins and themes by seeing what works or doesn't work for other people.
Another question here discusses specific software tools to support WordPress development. Here, I'm looking for more process and methodology that can be applied independently of tools, with the exception of certain tasks that might only be accomplished in a certain family of tools.