I used to be able to type in a lightning-fast way, while looking ahead (not down!) and walking quickly, on the Sidekick. I had every Sidekick model including a big bag of parts since, well, the older ones weren't super reliable. That said, I'd give anything for that experience again. In fact, as I typed this on an Android phone, I probably hit backspace at LEAST 50 times, corrected about 10 words due to typos (wprds showed up, with words as an option, etc.)
The size of my thumb covers about 8 keys.
The lack of physical keys may be amazing from a UI perspective, but for people who type quickly it absolutely sucks.
What's a shame is there's no choice.