It should also be the case that my work can disable/cancel my work account and be confident of no further work related access by me.
This is Fog Creek's org: https://trello.com/fogcreek
You'll just see our public boards, but we also have boards that are visible only to org members. Granting or restricting access to all of them is as simple as adding or removing a user. You can create and be a member of as many orgs as you want.
Not really a surprise. I'm having the same problem with a pile of services. The only thing I'm using that lets me switch easily is Gmail.
There was a post on here a month or so ago about a guy who lost his personal drop box because they do a bad job of understanding people have multiple personas.
We use Google accounts for work and Trello. That means that disabling the Google account is sufficient to prevent logging in to Trello, which is a good thing.
It also means that none of us can practically use Trello for personal stuff.