We're going out on a limb here to say that if these kinds of text input apps aren't the default smartphone keyboards in the very near future then we should all be banned from touchscreen phones and forced back to using rotary diallers.
SlideIT Lite is a free app available on the Android Market, Nokia Ovi Store and for Windows Mobile, which installs an alternative to the standard on-screen keyboard for text input. Once installed you might be surprised to find a remarkably similar looking keyboard in the place of the standard one, but instead of tap-typing out the letters you want, you simply slide your finger from one letter to the next to create your word. In words that have double letters, like the word "happen" for example, you only slide to the double letter once and let the software figure out what you are trying to say.
We've only had a chance to play with SlideIT on Android at this time, as Swype is currently in a closed beta testing period, but from what we know about the two apps, SlideIT seems to be a nose in front. Not only is it freakishly accurate, but it offers a shortlist of suggestions when you complete a word and it automatically generates a space so you can go quickly from one word to the next.
Seriously, if this style of text input isn't in the next iPhone we'd be both very surprised and seriously disappointed.