[UPDATE: I stand corrected. Informed commenters point out that though the source was available, MT was never technically "open source". To quote Richard Blain, "I was misinformed" -V]
It's ironic, to me at least. When I first got interested in blog software, I heard that Movable Type was the one to beat. It was written in Perl, which was my language of choice; it was open source (so you could make your own modifications); and it was by many accounts the most advanced blogging software out there (but not without argument, of course, this is the Internet).
Five minutes after I discovered it, the company announced that their 3.0 version would carry a new, commercial license. Suddenly being Perl was useless, because I could no longer modify, fork, or crib from the code. I moved on, and finally settled on Wordpress.
Now, Movable Type is once again opening its source code. Thanks to Ben and Mena for contributing this code back to the community. Ultimately, open source software is not about the software, it's about the community of users, and we users appreciate it when the companies we support share with us. Keep up the good work!
