We have “Blog Migration Documentation” at http://blogger.psu.edu/gethelp, but I thought I should walk the talk.
First, I found earlier that the export files from IE7 are funky to say the least, so I used Firefox (and documented this new quirk). The other gotcha is that you have to Publish (circle arrow button in top menu) in order for the new entries to appear – unfortunately the system does not prompte me (sigh).
In terms of logistics, my big concern was that I not loose my custom widgets. You have to create a new blog so you can import and configure it, but you still want access to the old blog, so for me the key was hold off publishing the new blog as long as possible. Ignore the publish messages until you are ready, then press the circle arrows at the end.
But as you can see – I’m up and running on this blog. The other ones might be trickier because I really did create custom styles and tweaked the template.