Recently I have stumbled upon a trick that will allow you to view only your running applications within the dock. The Terminal command was:
defaults write com.apple.dock static-only -bool TRUE
This would hide all of the "pinned" apps that were on the dock, and only show the active/running apps.
When I found out I was ecstatic, but slightly cautious (due to the fact that it may not be reversible).
I changed TRUE to FALSE and saw that it could easily be changed.
Now, for some reason, the Dock won't change back. I've tried running the command as root, rebooting, restarting the Dock, restarting the Finder, restoring TEMP files, closing and opening all running applications, and more.