I use pause/break quite a bit
Scroll lock ... I use VERY rarely,
At work, it is handy sometimes within Lotus Notes, but, hopefully we won't be stuck with that heap too much longer....
At home, I used to use it when I ran 2 computers on my desk with 1 keyboard/mouse to control them (was using Synergy, and had slackware box and windows box side by side sharing keyboard and mouse).... scroll lock would essentially tell synergy "stay on this PC", Was usefull when gaming to prevent accidently scrolling to the other PC which would then defocus the game...
I use insert frequently
I don't have "right click" key, or "windows" key, since I use an IBM Model M keyboard.
Also, I use the Dvorak layout, and I've pulled all the caps off of the keys, that way, if I switch to QWERTY, I'm not quite as confused as if the letter caps were there, but in the wrong place.