Heck, last night I was trying to use Anagram to see if I could easily save contact info from Facebook into Outlook. It wasn’t working. Turns out that it’s very hard to get data OUT of Facebook. (Anagram is a cool utility to grab emails, Web addresses, and other info off of emails and Web pages and add them to Outlook’s contact manager).
First, he notes that Facebook isn't terribly open - data goes in, and it doesn't come back out. You're left with the screen scraping kind of access that Jon Udell has written about so often. He then goes on to still call it open:
Look at how that cool new Google Reader app works inside Facebook. Data comes in, but it doesn’t leave.
That leads me to why Facebook is cool and AOL wasn’t. Facebook is somewhat open where AOL wasn’t open at all. Facebook is evolving rapidly because they opened up to third-party developers where AOL didn’t open up to third-party developers.
By that token, any proprietary application is "open" if third parties can write software for it. I think I'm still confused :)