Small use case to address your first question, but that I used all the time in school (and occasionally now at work): because everyone had the Dropbox client installed we would just create a shared folder that we'd all contribute to. Maybe only a couple of people ever had the Google sync client installed, and it was a lot more friction to upload/download files all the time.
On the converse, whenever we collaborated on an actual text document or presentation, we'd turn to Google Docs to do it, then when finished convert it into Word/PPT and stick it in Dropbox.
On the converse, whenever we collaborated on an actual text document or presentation, we'd turn to Google Docs to do it, then when finished convert it into Word/PPT and stick it in Dropbox.