I've signed up to Mastodon. You can find me here: @email@example.com.
I've known about Mastodon for a long time, I really like the distributed concept. I hadn't signed-up before as most of my friends were very active on Twitter. It's the "Social Networks are like Pubs" analogy again.
I guess the reason for signing up to Mastodon now is an attempt to step outside of the (perceived) echo chamber and my comfort zone. I remember the excitement of Web 2.0 (circa-2005), trying out any new service that came out. I think that along with IndieWeb, I'm trying to rediscover my excitement for the web, (and controlling my own content and data is a great motivator).