Google is giving away a free (plus the cost of a stamp) Gmail-related sticker kit, including a page of stickers for your keyboard to train your fingers with the popular email client's handy keyboard shortcuts.
According to the blog, the adhesive from the shortcut stickers "is a bit more removable than standard stickiness, so you can take them off once you've trained your fingers." Just send a self-addressed stamped envelope to:
P.O. Box 391420
Mountain View, CA 94039-1420