Frame.io has now been around for a few months and already had over 30,000 users. They now have a desktop app that integrates into FCPX and makes it really easy to share the timeline or part of it with collaborators and team members.
Frame.io is kind of a better hybrid of Dropbox and Vimeo. It provides for very fast upload of video files, makes sharing easier with collaborators and team members and provides an integrated commenting system that is tied to the timeline so that comments are synced to the video exactly. This alone makes Frame.io a better way to work that uploading video to Dropbox or Vimeo and then using email communicate with collaborators by sharing links and timecodes that people often get wrong. The system supports versioning and makes this very easy to work with, including synchronised playback of two versions for visual comparison purposes in a web browser.
Now with the app for Mac OS and FCPX this process is more integrated into FCPX and you can easily share the timeline in whole or part, particular clips, etc with collaborators. Support for other NLEs is not there yet but underway.
We are just starting to work with it and so will have more to report down the track.