* Migrating one's account and tweets to Mastodon
* Finding people on Mastodon
* General confusion about what federation is, or what it means
* Stories of people who once used a Mastodon belonging to a friend group, had a falling out with whoever happened to be running the server, and was kicked off/had their account deleted
* The fact that DMs aren't private, and can be read by an instance admin, or by the instance admin of the instance of the user you send them to. This particularly seemed to unnerve people because you're more likely to interact and know who the instance admin is than you are with Twitter support/SWEs.
* The difficulty of choosing an instance.
* The difficulty of avoiding certain people and certain content, usually spoken of in terms of principle: that is, abusive messages and content which admins must agree to filter, but some admins may not want to block that content, leaving the users on an instance known for harboring that kind of content
* On the flip side, rampant defederation and the formation of cliques which become increasingly isolated social bubbles.
* The name of the software and its default interface
* The names of various instances which range from the whimsical to the offensive (e.g. 'wolfgirl.engineering' to 'fuckonthefirst.date').
* GDPR concerns and personal data privacy concerns - how do I delete media and text that I've uploaded that's now been shared across multiple instances? How do instance owners cope with this under the law?
I've seen very, very few responses to any of these problems; some of them I object to myself, but it seems short-sighted to say that the only reason people aren't jumping ship is because of network effects and not genuine concerns with the technology and the community as it exists today.