I stopped by the 4iThumbs booth to check out their product that would purportedly increase my (admittedly dismal) typing speed on the iPhone/iPod touch. It consists of a plastic overlay that puts small ridges between the letters of the standard iPhone keyboard, available in both portrait and landscape formats. The product comes with some tabs that you affix to the top and bottom of the device, and you can then slip the plastic overlay on and off. You can touch through the overlay and use the phone as usual while it's attached, although the bumps aren't terribly comfortable for swiping. There's a matching set of tabs for the back of the device which can hold the overlay when it's not in use.
I tested it out, and it works. I never texted much on any device other than the iPhone, so I can't make a direct comparison of typing speeds between an iPhone and, say, a Blackberry. I do type a lot on my iPhone, though, and I can readily say that my typing speed and accuracy increased dramatically while using the 4iThumbs overlay.
4iThumbs is $19.95US online for 1 set, which includes portrait and landscape versions and the tabs to attach them to your iPhone/iPod touch. At Macworld, you can pick up 2 for $15US, but you'll have to get there quick to take advantage of the show pricing.