I think I normally type around 80-90wpm and can normally hit 110wpm on those silly typing speed tests (my record is 117wpm typing a passage from Terry Pratchett's "Reaper Man").
I had been bracing myself for a big period of adaptation but I was happy to discover that writing english prose and E-mails was actually not too bad to get used to - apart from the different fingers used to hit the B and N keys. It took a lot of effort to undo ~20 years of muscle memory! In some ways that was even harder than learning the somewhat alien (albeit logical) layout for numbers and symbols. In any case, after 1-2 weeks I was pretty happy with my progress and didn't consciously feel frustrated doing E-mail and doc writing, although I've yet to break ~65 wpm.
Programming was another story. At the time I was working mostly in perl, a punctuation-heavy language. So it was more like 6 weeks before I felt that I wasn't struggling all the time.
The mouse emulation kinda works but not well enough to rely on. Thanks to this I installed and am now a full-time user of the Pentadactyl plugin for Firefox
http://5digits.org/pentadactyl/ and vimium in chrome (I prefer Pentadactyl though, even if it's annoying as hell).
Fun fact: my brain seemed to be re-wiring the B and N keys for *all* my keyboarding use. I eventually found myself using the wrong fingers (thus hitting the wrong keys) whenever I went back to using a normal keyboard.
That's gone away since I've been using "normal" keyboards at my last couple of office jobs, mainly because I'm nervous about starting conversations around overuse and RSI. Sadly I've seen a few employees make a lot of noise about overuse injuries and that's somewhat impacted them negatively because managers tend to think of you as a liability...
