I don't know why anybody would run a vanilla server for any other reason than to play with their trusted friends. There are many useful/amazing plugins in Bukkit that I consider "must-haves" but I could probably live without most of them if I had to. The real problem is that people are evil. With vanilla, there's no way to detect and/or prevent hacking and griefing. So why doesn't Bukkit team up with Mojang to make Bukkit the new vanilla server? They're already working together, aren't they? Mojang said Minecraft will have modding support. If this means server-side modding then they would re-invent the wheel. There's probably some crap legal reason not to do it, but it'd still be a good idea.