I have taught CSP the last two years and I have not done a summer assignment. Really for some of the same reasons Andrea mentioned. I personally haven't had as much issues with getting through all the content. I work in a public school in the suburbs of MN, so we start after labor day but at the same time, for most of my students this isn't their first AP course, so they are ready to get to work in class.
I have heard of people assigning parts of the Blown to Bits book as a summer assignment. The reading level is somewhat high on it, so keep that in mind if that might be a barrier for some of your students.
I love the idea of doing jump start days right before school starts, but that would be a no-go in our district. Also, student athletes are doing a lot of work around then which leads to another equity issue...
One last thing to consider is that code.org's curriculum operates under the premise of introducing concepts before vocabulary. This is pretty cool to watch in classes with larger gaps in previous knowledge. Essentially, it allows for a low floor - everyone can engage! At the end, when you introduce vocabulary, even students who know what TCP is have an "a-ha" moment, they "feel" what TCP is (rather than just understand what the definition is).
I'm also interested in what others think here!