Probably due to #TwitterDown, Mastodon is currently seeing an increase in new users to around 1000 new users per hour, from the normal recent baseline of around 300. This is nowhere close to previous surges which reached as high as over 5000 per hour.
As has been noted, many users created accounts here and drifted back to Twitter. It seems many of these existing accounts are reenergized, so the actual impact of this latest meltdown may be greater than the numbers indicate.