The joke internally is that Dropbox asks lots of concurrency questions because the Dropbox client has 50+ threads :-)
That said, I think what I noticed at Dropbox is that asking lots of tough questions gets you a lot of pretty talented folks who are very interested in solving hard technical problems. So from an infrastructure side, Dropbox was overflowing with talented people. From the product side, though, it was harder for teams to staff frontend projects or make progress when their ideas were challenged by infra.
That said, I think what I noticed at Dropbox is that asking lots of tough questions gets you a lot of pretty talented folks who are very interested in solving hard technical problems. So from an infrastructure side, Dropbox was overflowing with talented people. From the product side, though, it was harder for teams to staff frontend projects or make progress when their ideas were challenged by infra.