I’ve been running an Emacs built from bzr for a while now. I did this so I could try a newer version of Semantic; the one in Emacs 23 is just too broken to use.
Semantic, in case you haven’t heard of it, is an ambitious project to turn Emacs into an IDE. Really it is quite a crazy project in some ways — it includes its own implementation of CLOS (which opens a strange Emacs maintenance debate: how can CLOS be ok but the CL package not be?) and a port of Bison to elisp (but again, strange: the port is really a pure port, it does not use sexps as the input — bizarre).
Semantic is now usable in Emacs — I’ve found a few buglets, but nothing serious. In fact, now I find it indispensible.
I have it configured in the most Emacsy way of all: I didn’t make any changes, I just enabled it with
M-x semantic-mode. Then I visited a bunch of gdb source files. Semantic started indexing them in the background.
Now when I want to jump to a declaration or definition of a function, I use
C-c , J. The key binding is nuts, of course, but I’ve been too lazy to rebind it yet. Anyway, this acts basically like
M-., except you don’t have to ever run etags. Wonderful.
Semantic has some other nice features, too, but I haven’t really used them yet. If you’re using it I’d love to hear what you do with it.