There’s nothing hard coded. I just downloaded the new version and my install with half a dozen authors and a couple dozen blogs works fine just as it did. The licenses are all on the honor system.
That’s a quote from this rather active MeFi thread about MT3 Licensing. So if I did upgrade, I wouldn’t be in such a bad position. But still, WordPress is looking like a much nicer concept, though any move will have to wait until the bulk of my exams are other since the transition will probably take quite a while (including setting up redirects and whatnot).
In any case, if I do, this entry has some handy links to help me.