A colleague of mine re-introduced me to Vim about 6 or so months ago. Like many people, I dismissed it originally as entirely too obscure and unnecessarily difficult to use.
However, as a programmer I've come to appreciate the powerful UNIX command line well-over the windows one. It only seemed logical to apply the same thing to my editor (command-line vs point-click)
The h-j-k-l keys are used as left-up-down-right movement keys because they are on your 'home' row and hence quicker to get to (and come back to). As a touch typer I can really appreciate that!
One interesting thing I've noticed is that after 10+ years using the arrow-keys I sometimes unconsciously hit the 'p' key (which means put or paste) instead of up when using these keys. :)
This is weird because I'm using my little finger - even though I use the middle finger for up-down when on the standard arrow keys...
It's something like 'spatial' body memory controlling my fingers!