There is indeed the problem of discovery that Mastodon doesn't feel like addressing. Like, you pick a server, make an account and now what? There's no way to bring your existing social graph with you. Even if your friends are there, you won't ever find them without asking each and every one about their username@domain. But I have some ideas on fixing that for my fediverse project — like making a DHT out of instance servers, thus making global search possible while keeping the whole thing decentralized.