I thought I'd write down one of my favorite vim tricks. This one is to change or comment a vertical block of text all at once, instead of one line at a time.
* Step One
Enter Visual Block mode with "Ctrl+V", then highlight a single character wide slice you wish to add comment characters to.
* Step two
Press "Shift+i" to enter insert mode, then enter your comment character. Don't worry, this will only effect one line at first.
* Step three
Press "Esc" to apply your change to all lines you previously had highlighted.