I do occasionally wonder about defecting to Emacs from my current choice of Jed (which is basically Emacs-like in its key bindings but completely different under the hood). At the time I made the choice, Jed had far better syntax highlighting and was considerably smaller and faster; these days Moore's Law has rendered the latter points largely irrelevant, Jed's syntax highlighting has got noticeably worse, and I imagine people have been hard at work improving Emacs's.

My primary reason not to is that I'd have to translate ten years' worth of accumulated editor configuration written in Jed's embedded scripting language, including my personal MUA...

You might want to have a look. Emacs went through a bit of a doldrums in the early 2000s as it took six years to bring out version 21 *. But now it seems back on track, and if you used to be a fan, but haven't used it since version 20 I think you may be pleasantly surprised with version 22.

* Native windowing system integration was pretty tough, but I think the big problem was Unicode. Emacs was a victim of being a first mover here: in the 1990s it had adopted its own system (MULE) for integration of multilingual character sets, so when Unicode turned out to be the standard way to achieve this, MULE had to be backed out while the rather complex interface remained backwards compatible to avoid breaking a vast installed codebase.

Jed's syntax highlighting has got noticeably worse

That must have taken some special effort.

Do you really mean, worse in absolute? Or merely "not as good as what other programs offer these days"?

If the former, I wonder what made people take something that works and make it worse.

Yes, I do mean worse in absolute terms. What happened was, there were two separate highlighting mechanisms in Jed. One was a sort of ad-hoc thing hard-coded in the editor's C core, which was basically just about usable for highlighting C and could also be extended to other basically programming-language-shaped syntaxes by configuring it at the general level of "this is the comment character, this is the list of operators, these are delimiters etc". The other was based on regular expressions and was much more flexible and general, and in particular one could configure it entirely in the customisation language to be suitable for things that had nothing at all to do with programming languages. I had hoped that highlighting schemes based on the former would gradually migrate to the latter and then the former would be thrown away, but it appears that in fact the latter has fallen into disuse and more and more language modes are reverting to the (now somewhat souped up but still not really as flexible as it should be) former. I think part of the reason for this is that the maintainers didn't really understand the regexp-based scheme, so when it came to adding new features they tended to graft them on to the one they knew how to modify.