Strangely enough, Vim is part of the trendy Mac / Ruby / polished websites with exclamation mark and one button setup. That may explain this revival atmosphere. Why strange? Why, Mac setup is supposed to be beautiful and easy, Vim is neither.
OS X is popular among hackers because it's both a Unix-like and polished/supported enough to use as a "serious" workstation (not that Linux or *BSD can't make a decent desktop, but most would rather spend time writing code than config files).
It's really just about having an operating system that provides everything you need without having to worry about it, because as a programmer your time belongs with the applications. And when it comes to applications, you choose the right tool for the job (enter vim).
That's why I use Ubuntu.
I like to think learning Vim akin to learning a musical instrument. It's not easy, the learning curve is very steep and it forces you to think about writing code in a completely different way. But once you get the hang of it, the power available to you is absolutely incredible and you'll code with efficiency never thought possible.
My 2 cents.
In fact, this reminds me French painter Braque being shown a fake Braque, he said: "this is not my work, it is beautiful". What I mean is that "beautiful" in the common sense, the one that applies to clothes, girls, gadgets (including Apple's), commercial movies, 3D games, etc., this superficial aesthetic quality not important.
In this sense, Vim, with it's fixed width font, black background, pure-text help, etc. is certainly not beautiful, and therefore a bit of a stranger on a Mac where, apparently, so much money and neuronal activity has been spent to beautify its OS, its casing, its font aliasing, every single icon and even its boxing.
Gosh, look at the Vim logo and tell me by which miracle it can have so much sex-appeal in a Mac environment? (Or has it? dasil003 says no in an uncle comment, maybe he is right.)
Notice how I said it 'can be'. Out of the box, Vim is not very attractive, but with a bit of work it actually looks rather nice (yes, I did modify the application icon, but that's not really what I want to get at here).
Some of this beauty is subjective due to the syntax highlighting used, configuration of invisibles, etc, but that's configurable and therefore can be customized to your liking.
There are clean and elegant fixed with fonts, which again, you can choose whichever you prefer.
What I meant by simple was the complexity (or lack thereof) of the UI. It only shows you some basic information that is readily important, everything else is hidden away in various keyboard shortcuts. This makes it more complex to use, but it also means the beauty of your work, the code, is at the forefront with little distractions. Hell, I even turn off scrollbars.
At the risk of starting a discussion of opinions over my choice of syntax highlighting, here's a screenshot of my vim setup:
http://dl.dropbox.com/u/18782/macvim.png
I don't really understand how you can call this ugly, unless you're referring to my taste in syntax highlighting.
So, my first point still hold, where Textmate is a ease, Vim is a kind of an intruder in a Mac / Ruby / Designer-first set-up.
Vim does EXACTLY that. It doesn't add silly buttons that require you to remove your hands from the keyboard to the mouse to interact with. It doesn't add silly gradients that get in the way of showing you text. Aesthetically it's incredibly simple, and interactively it's incredibly complex, but IN A GOOD WAY. Not everything, especially tools, should be easy to use and learn. A well designed application knows its target and exploits it. Vim does exactly that. It doesn't mean it's a catch all tool for everyone, generally those kinds of tools end up half assed.
And for the record, I am actually a designer, I used to use TextMate, I now mostly use Vim. The UIs are similar in their sparseness. The 2 small beefs I have with Vim is the title bar text being overly verbose and and the rounded corners added by Lion on the bottom are rendered a bit glitchy.
TextMate on the other hand, while a decent text editor, has perhaps the most hideous project drawer around. Wait, actually, TextMate was never 'designed' as you describe it either. It just uses built using Mac OS libraries. I would think that if you were going to harp on design so much you would at least bring up the more 'designed' text editors, like Coda and Espresso, not TextMate.
In my case I probably never would have switched if TextMate 2 hadn't been extended vaporware. What it made me realize is that I'm fine using a commercial OS like OS X, or a trendy framework like Rails as long as it's suiting my needs in the short-term. But an editor is my core tool across time and space. I need it to be available on any platform, and be well-suited to any language I might learn in the future, working well over an SSH shell is also a huge bonus (and how I got my feet wet in vim 15 years ago). I appreciate aesthetics, but it doesn't trump pragmatism, and I think many rubyists feel the same way.