Vimium brings me one step closer to never having to use a mouse. Hints mode and vim-style navigation keys are my favorite features. ? (shift-/) brings up a handy shortcut overlay. A must-have if you live in vim.
If most of your interaction with the computer is done by typing - in a text editor or at the command line, for example - then being able to use the keyboard for those other actions like switching tabs, scrolling windows, opening files, etc. allows you to stay in the same "input mode" for longer chunks of time.
I'm not so familiar with vim, but it seems that it's so popular because of all of those keyboard shortcuts allow people to interact with the computer consistently without having to interrupt their "flow".
If switching from mouse to keyboard (or vice versa) involves a little bit of extra cognitive processing, that adds up over time and can make your experience just a little bit slower and more frustrating. I guess switching between different keyboard shortcut schemes can have the same sort of effect, so having those same mappings of keystroke(s) --> computer action(s) available across multiple programs must be satisfying to the people who have adopted them.
Anyway, the gist of what I wanted to say is that when you use vim, you do a lot of thinking about how you're going to position the cursor or exactly how you're going to do a visual selection of some chunk of text. When you use something like Acme that's mouse oriented, you mostly use the keyboard to enter text, while the mouse is used to point and select text. Changing the cursor is a visual, spatial thing, as is selecting text; the mouse is ideal for this, being a two-DOF system, while the keyboard is a discrete/linear tool.
I'm a huge fan of Acme for most of my editing, but I like vi for quick stuff, plus there's a certain charm to firing up my old VT-220 or ADM-3 and hacking away. However, when I see somebody trying to do serious editing in vim, flailing away madly to move the cursor to the right place and do that funky funky visual selection thing, I get impatient and a bit ticked; he feels busy because he's slamming all these keys, but I just keep wondering what the hell is taking so long.
Vimperator and this new Chrome extension have a good idea in providing keyboard shortcuts that are both extremely brief (one keystroke, no need for Ctrl combos) and pretty familiar to people who use vi. However, people should be mindful of the best uses of all their input devices, not merely the keyboard (which is certainly more 1337, but not always the best choice).
One time, I was working on something important, and every ten minutes or so, my girlfriend would interrupt me to tell me about something that she was reading... finally, after the third or fourth time, I got really frustrated, and as a systems guy, naturally, I yelled, "CONTEXT SWITCHING IS EXPENSIVE!"
She didn't get it... but she got it.