Expanding on the Typing Period Quickly Tip posted by David Pogue earlier today, iPodHacks notes that the same sequence can be used for the shift to to allow you to quickly capitalize a letter without disrupting your typing.
Just touch the shift key and then slide your finger across the screen to the target letter. Your moving finger will trigger the confirmation pop-ups for the letters you're swiping over, and the letter under your finger when you lift off the screen will register (or be typed), in caps. Smooth caps!