Typeracer is something I did quite a bit a well. If you don't have to read the stories any more you know you're practising enough. A program I really like is TypeFaster. It forces you to use every key on the keyboard which is mainly relevant for the keys you wouldn't be using all that much in regular sentences. And in case you're really getting bored you can always try The Typing of the Dead.
Not exactly sure how long it took me to get up to 30 WPM, but I'm quite sure it was at least a week. I had the added benefit of having just tried dvorak a week before that which may not have helped either.