In addition to
importing ratings from IMDB, you can now import your ratings from Flixster and Rotten Tomatoes. To do this, go to
your ratings, and click on either
Import from Flixster or
Import from Rotten Tomatoes links at the top. Copy-paste the link to your Flixster or Rotten Tomatoes user profile in the text box and click on the Import button.
Update
The Rotten Tomatoes importer has been separated from the Flixster importer.