From the FAQ (and I fuckin’ quote):

The question of what a “weblog” is is somewhat muddy, but the basic answer to the first question is that, if you’re using multiple “Weblogs” in Movable Type in order to build 1 site, that only counts as 1 weblog towards the license limits.

In our licenses, we now address this with this language: “Weblog” means a single Web site viewable at a single URL (Uniform Resource Locator), consisting of one or more weblogs as generated by the Software via the “Create New Weblog” function of the Software.

So does that mean that if you keep one “weblog” that’s comprised of three sites w/in Movable Type 3, but is published at many URLs (e.g. a main URL and at least one additional URL for each entry’s individual archive), one would need a “weblog” “seat” for each “URL”?
Clearly not, but I always recoil in fear when I see such imprecise language in a redaction of an existing fubar’d document!