This is nothing new to old-timers, but thought I'd bring it up for newcomers to vi editing....
In Tc / Pi / dCore, we do a lot of configuration file editing. This usually involves copying a line, editing in some changes, and remark-ing out the original line with a hash # at the beginning.
Most vi tutorials cover the "yank" and "put" features quite well, but I'm amazed at the amount that don't mention the three-fingered salute - and that's not ctrl-alt-delete!
What I'm talking about is Y-Y-P, or yank-yank-put for instant copying of the line you are on.
I only mention it since I see this quickie combo often left out of many tutorials.