Having used a Treo for 2 years, then an iPhone for 2 years, then most recently a Palm Pre, I have two more observations to make on the buttony-vs-glass keyboard issue which I haven’t seen made elsewhere.
1) Not just foreign languages: even in English, anything that isn’t a word doesn’t benefit from autocorrect, and I find it relatively easier to type on a physical keyboard without autocorrect than an onscreen keyboard with autocorrect. I notice this with: names, swear words which aren’t in the dictionary, abbreviations, passwords, and code snippets. The onscreen keyboard with autocorrect does a pretty awesome job with dictionary words (I think it’s instructive to note, here, that T9 also handles this case, if not perfectly, at least surprisingly well). Another, possibly less contrived, case, which pisses me off if I’m trying to be meticulous — capitalization. Sometimes I type ID and I want it to look like that either as short for identification or for Idaho, and turning it into I’d isn’t cool.
2) After using an iPhone for 2 years and after initial reluctance finally giving myself over to it, I found I could type about as fast as I could on the Treo keyboard. But, at a much higher cognitive load. On a full-size keyboard I can pretty much type without thinking, and to some degree can hold a conversation and type a queued thought at the same time. On a physical cell phone keyboard i.e. Treo, typing requires more concentration but I can still queue up bursts of keystrokes while doing something else. Typing on the iPhone, even after 2 years, generally requires all my concentration. Partly because I need to watch the keys to see that I hit the right ones, partly because I can’t always trust autocorrect (and with low but still annoying frequency, it’ll take something I typed correctly and turn it into something else). So I don’t find a hardware keyboard to be particularly faster, but I do honestly find it to be less stressful. I can type the same thing at the same speed with less mental load, more confidence.
(Overall, the Pre keyboard is not as easy to use as the Treo’s, but I still find the above two points to be true of it.)
I also don’t think this really changes Gruber’s (a) and (b) conclusions in his second article; Apple’s not going to add a hardware keyboard to the iPhone and they’ll still have plenty of customers. That doesn’t mean I have to like onscreen keyboards, though.