Sturgeon’s Law: 90% percent of everything is crap
FizzBuzz is such a trivial problem that it’s almost insulting to ask an experienced developer to do it. It also solves a specific problem of the hiring processes, which is that a few “developers” were slipping through the system, having the right resume and saying the right things in the interview, and then turning out that they couldn’t code at all. By making the candidate write code even for a trivial problem, you wash these people right out.
Playing multiplayer games on the Internet gives me headaches. Too many asshole kids griefing the whole experience for everyone else. So when I wanted to get back into Minecraft recently, I looked for a server with a whitelist. What did I need to do to get on the whitelist? Answer a few questions on the forum post by the server’s owner. That’s hardly any work at all, but it’s more than most random griefers are going to do. That tiny amount of trust added to the system keeps them out, or at least makes them easier to deal with.
When I wanted to play GT5 in a group, I found a racing league on Reddit, where I had to add the organizer as a friend and show up at a specific time. Anybody with a Reddit account and a PS3 could have done the same, but it keeps out people who are deliberately ruining the the experience for everyone else. Even if accidents happen (I certainly caused my share), everyone is at least playing in good faith.
These barriers to entry are tiny, but may improve the whole experience to a greater degree than anything else.