I've worked on the Dropbox client back in 2009 and I can tell you that Dropbox has spent considerable resources optimizing Python, so there is actual python-related work to be done.

As Rian Hunter mentions they've for example implemented a custom memory allocator: http://highscalability.com/blog/2011/3/14/6-lessons-from-dro... and that's just one part of it.

With a few hundred million installed machines or so, having Guido on board to make python work better for Dropbox-scale apps is a huge win for them (and python)!