I'm following the discussion around the upcoming 2.0 release of the iPhone, combined with the anticipated hardware refresh that will undoubtedly bring 3G to the plate and have noticed that the missing keyboard meme has come back around. I think that (as usual) Gruber covers the major points nicely, but there are a couple of additional things I'd like to address.
The first one has to do with localization. I live in France and communicate in both English and French on a regular basis with my iPhone. I used to have a Blackberry and liked the well integrated email and calendar support although very efficient for email, the calendar left some room for improvement. My major beef is that when you sell an item with a hardware keyboard into a localized market you make a pile of assumptions. Most notably that the user will only ever need to write in the local language. I realize that I'm a bit of a niche market, but I suspect that the higher up the chain you live in Europe the higher the likelihood that you converse in multiple languages and the higher the likelihood that you use a smartphone.
I found the Blackberry keyboard to be pretty nice, although I was coming off a Treo 650 keyboard so the subtle differences kept tripping me up for the first couple of weeks. My major issue was the moment that I needed to start writing in English. The Blackberry would helpfully try to correct my text as if I was writing in French. This brought about much use of colorful language (often not found in the Blackberry dictionary either). I lost count of how many messages I sent with the word "thé"* in place of "the".
On the iPhone you can make multiple keyboards available under Settings > General > International > Keyboards. If you have selected multiple keyboards, an additional key that looks like a globe will appear to the left of the spacebar and tapping it toggles between selected keyboards. With the toggle also comes a change of dictionary for the auto-correction features. For some reason that I don't yet understand, I find that switching between soft keyboard layouts relatively easy whereas switching physical keyboards induces a lot of errors while going through the adjustment/training period. I currently switch multiple times/day between the different layouts depending on the context and have discovered that the one finger tap approach can adjust on the fly once you've mastered the basic technique.
The biggest hurdle of a Treo or Blackberry user has in mastering the iPhone is that you don't keep your fingers in constant contact with the keyboard and use a slide-pressure-slide-pressure technique to typing. You have to get your finger into and out of the detection field. This is where I see Blackberry habitués getting frustrated.
The second point has to do with haptic feedback. I think that there is some really interesting work being done in this space that will change the feeling of using a virtual keyboard. Interestingly, when you google "haptic feedback keyboard" almost all of the links come back with stuff regarding iPhone prototypes (plus a couple for Nokia). Personally, I think that Apple is pursuing this kind of thing more for the gaming applications than for additional ammo to sway current Blackberry users, but hey "two birds, one stone" never hurt.
* French for tea.