|Extra recipient field goodness|
It opens a new draft email with the cc: and bcc: fields already expanded. I accept cash, credit card, check, PayPal, or wampum.
I think what I actually feel most mystified about is that upon pressing shift + / (also known as "?"), I fail to find any shortcut listed. Yet, I guarantee you will see a similar result if you press "b," while outside any text box in Gmail.
You may now applaud. Thank you.
UPDATE: It's been brought to my attention that there is actually another variant of the undocumented compose email function: d. D does essentially the same thing as c or b, except for that d opens only the to: and cc: fields. Thanks for this additional shortcut, Alex!