Moving out blogs from one WPMU install to another

This is definitely a beginner question. I’m planning on starting a single WPMU installation, which will host blogs from a few companies.

But if one of those companies wants to move its blog to another server, how hard is it to move a blog, with all posts, users, themes, plugins, etc. from one WPMU install into another one?

Basically, I’m trying to decide if it’s smarter to start with one WPMU install and only move a business in the event it wants to split off, or segregate the two into two WPMU installs because splitting them would be so much harder, later.