Dropbox is turning off its v1 API, which Flytext uses to access files stored in Dropbox. Flytext uses the Ruby library for this API on its server, and there is no drop-in replacement available for the current API. For this reason, Flytext will cease to work from June 28th.
It seems that there have been a quite a few satisfied users of Flytext over the years, and I apologise to all those who find the service useful. I can't recommend a specific replacement. Personally, I use Simplenote for notetaking across various devices.
So long, Steve