"No problem, we thought, Google is nice enough to provide a programming interface to support this. In fact, they have multiple such APIs (application programming interfaces). As it turns out, neither of the versions of these interfaces that Google provides works completely. One version doesn’t let you migrate comments (an important part of many blogs). The other doesn’t let you move more than a few dozen articles – period. Basically, Google has seemingly made it intentionally difficult to migrate off of their platform. This is just annoying. We ended up writing a fair amount of custom code and jumping through a few hoops to get all of the data migrated over (which we finally did). But, this was much harder than it should have been, and we’re trained professionals (so please, don’t try this at home). If you’re not a programmer, chances are you won’t be able to do this yourself. It shouldn’t be that hard."
I know that WordPress does a good job of letting you liberate your data and move it around; I’m thinking about moving the four or five blogs that I maintain onto a single server — the fact that all of them are either in WordPress already or are importable by WordPress is going to be helpful.