I've recently stumbled on Sublime Text and I'm purely amazed!
This thing is faster than Mono Develop and way more comfortable. It has some couple of awesome features, but that's not the main point.
I've seen a couple of Unity developers interested in this ( mainly Jacob Pennock ) and a couple of plugins already created and ready to use. It's pretty close to being a full featured IDE, but it still needs some work to be able to fully support the whole process. ( It can't build, projects for instance )
I'm currently working on a build system working with Visual Studios "devenv", which works but it's far away from convenient.
Anyway - Is anyone else interested in the whole Sublime Text Unity development?