I've never used kanban in a proper work setting - only the discussed the theory in the PM training. I think they are great on paper. You are right though they dont work well for those who can handle a bit more! they assume everyone has the same capacity and capability and therefore they are slightly flawed.
I think Kanban would be saying that no matter how good person x is at multitasking, compared to person y, you will find that person x working on one thing with their full attention is better again. A typical response is to say "I can't only work on one thing, I'd be sitting around waiting for other stuff to happen too much." To which Kanban would then say, "well, in that case, you should be looking at the whole process, seeing where those 'waiting around' delays are coming from, and working on removing them, until you *can* work on one thing without any problems." By juggling stuff to keep yourself busy, you are actually masking the wider inefficiencies in the whole system. The most important work you can do is to improve that system for the whole organisation, not just churn through your own bits and pieces slightly quicker.
There is lots of interesting stuff around this if you google (eg) "limit work in progress".
Of course, kanban's origins lie in manufacturing/assembly line stuff, rather than humans doing software development, so nothing's entirely prescriptive. But it's my favourite methodology, even though I'm still some way off doing it 'properly' (deceptively tricky for a simple concept!) And I totally agree with your point that:
every approach is slightly flawed and its finding the bits that work well in the environment you find yourselves in or dare i say the true lean approach of tailoring the approach to your environment!
A lot of the IT PM stuff is faddism, driven by the money-making opportunities in a new concept. The important thing is to understand the principles, adapt it to your environment, make it routine, and have lots of conscientious intelligent people. I've worked with very qualified PMs who were completely ineffectual; and people who had no PM qualifications at all, and weren't even on that role in the project, but were brilliant at it because they were organised and had bulldog-like tenacity.
In terms of recruitment, I'd put project delivery experience and attitude ahead of qualifications, myself. I appreciate that's not going to apply to certain types/sizes of organisations, though. But in some ways, it can be easier and more useful to try and take the initiative and insert yourself into this stuff in your current workplace, than do lots of courses and exams, if at all possible.
