From that point you'll be constantly learning new ways of doing things better because vim is really more of a language than anything.
The biggest, easiest, thing for me was macros. Being able to easily and quickly record a macro and apply it over many lines - that's slick. Like converting a CREATE TABLE to a set of ORM instructions, or into a structure. Before I'd use some half cooked regex and clean up after. Now I just edit one l line while in a macro then run it N times.
Apart from that, it's just a ton of little things that add up.
Also: ViEmu for Office. VimFx for Firefox (there's one for Chrome too, Vimium). Browsing without the mouse is really great; quite elegant.
Nowadays when using vim I occasionally have people ask me "how did you do that?" and I won't even know what keys I typed. The keybindings are as natural as walking/grabbing things and require as much conscious thoughts. I usually have to redo it in slow motion to see what I did...
I can highly recommend Bram Moolenaar's essay on "The Seven Habits of Effective Text Editing" (http://www.moolenaar.net/habits.html), it has a vim focus, but I think his points are editor agnostic
Edit: I started using vim as a windows GUI person in university since I wanted to edit over SSH and vim was the only editor with syntax highlighting on the servers. So it's not like I was a terminal wizard back then (I am now :p)