This gotcha got two smart people I know in as many days so it is making it to the blog:

Is a command line that used to work and that is exactly the same suddenly not working any more? 

Are you copying and pasting that command line from a Word document or an email that someone else sent you (because you knew you'd need it again)?   Does it look exactly the same as it used to be before but for some reason it doesn't work anymore?  If it was stored in a Word document before you cut and paste, pay very close attention to double quotes in any of the arguments.  It may be that the standard double quotes were automatically transformed into those fancy typographic double quotes along the way.  Unfortunately, even though they look prettier they are no longer valid to use at the command line.  One way to fix this is just cut and paste the command in, but befor executing it, delete the fancy double quotes and replace them with standard double quotes you type in directly from the keyboard.  

And here's another one for free that might help someone out there:

Is the F12 key not working when you boot up your brand new computer?  

Check your new keyboard, it might be one of those new fangled ones that disables the function keys on boot by default unless you press the rarely used but appropriately named "F Lock" key first.   Since there is no visual indicator of whether [F Lock] is on or off, one trick is to alternate doing [F Lock] [F12] [F Lock] [F12] [F Lock] [F12] during the boot sequence hoping one of them will work.   While doing this, maybe a good time to work on your imitation of Tom Hanks in You've Got Mail (when he was deleting multiple paragraphs using only the backspace key).