I have recently switched to emacs from TextMate. I have not been using TextMate to its full potential as I simply did not have the need to do so. It was good. It worked great out of the box.
Then I realized that I needed to do much more than just use a text editor and have been glueing a lots of other utilities together.
Then I doscovered emacs. A behemoth godknows how old. And decided to learn it.
The learning experience is really steep but I think it's worth it. EMACS survived the test of the time along with VI(m). But sometimes I just feel it's too much and the great extensibility comes at price.
I am looking forward to Atom but the performance is not that great compared to EMACS. Not yet.