When I left Tangozebra last year, I had various folders of emails that I needed to take with me. I did what seemed to be the sensible thing of exporting them as Outlook .pst files, copied them onto a machine that was going with me, and thought no more about it.
Then, when I needed them, of course, I couldn't open them. I have Outlook 2002 on my machine at home, but these needed Outlook 2007. Fortunately, there's a demo version you can download and play with for 60 days - long enough to get the data off, but not long enough to just keep them all in Outlook. So I was looking for a way of exporting emails. Outlook actually has a way of doing this, although it's not really practical for the thousands of emails I've accumulated over the years that are important; however the export feature isn't in the demo anyway, so it's somewhat moot.
I scrobbled around the internet for a bit, finally chancing upon a tutorial and sample script for exporting data from Outlook using Python. It uses the built-in email-as-text export feature of Outlook, which frankly is pretty unappealling, lacking as it does most of the headers, and in particular useful things like email addresses. Also, their script outputs emails as individual files, which again is unhelpful: I just want an mbox per folder.
So I wrote an Outlook email reaper. It's happily exported about 4G of emails, although it's a long way from perfect. See the page above for more details.