Interestingly, it's hardly an hour since he announced the news on Twitter, and it is already mentioned on his Wikipedia page:
Wow. Quite a surprise. But see Black Swan.
My initial reaction: First and most important thing, of course, is that Dropbox should let him keep on spending a good amount of time working on Python, as he did at Google.
Python is more important than any one company, considering its impact and usage worldwide. He's the BDFL for solid reasons.
I had blogged or tweeted some time ago that Dropbox uses Python a lot, to write its app clients on different OS's.
- Vasudev Ram