I came to the iPhone after never having used a Blackberry/anything of its ilk. I found the keyboard dead easy and I can zip along on it just fine. (Rule number one: touch lightly. It doesn't take much. If I can accurately hit a link on a non-magnified page in what would be about the equivalent of a 5-point font, it's sure as hell possible to hit the right key on a much, much bigger keyboard.)
Since then, I've been handed someone else's Blackberry to enter my contact info. I found the keys perfectly usable but the navigation & methods for getting to special characters more than a bit clunky. I'm pretty sure long-time users wouldn't.
So... to each their own, basically, but I'd be far more interested in the first impressions of people who'd never used either type of phone before, because of course
your existing assumptions are going to skew things. Methodology 101.