The short problem: many frequently-used keys, such as the comma and the period, are on an alternate keyboard, requiring several clicks to type in.
The short solution: touch the .123? key but don't lift your finger. The alternate keyboard will quickly appear. Don't lift your finger yet - instead, slide to the character you want and release. You'll get the character, and the keyboard will automatically switch back to the QWERTY keyboard.
Fantastic - thanks David! And thanks Tori for forwarding it to me :)