Slate Magazine was granted access to Rotten Tomatoes’ vast movie database and they found some interesting results about movies released since 1985. They include:

• The average actor has a Rotten Tomatoes score of 55% in his first film it then steadily drops to 50% for his fourth film and it stays there for the rest of his career
• Director’s first films are also given an average score of 55%. But instead of getting worse with time they seem to get better with experience. By the eight film a director’s rating jumps to 63% and after that it jumps again to stay between 80% and 90% from the twelfth film onwards.
• French actor Daniel Auteuil was the highest rated actor. John Ratzenberger, a voice actor frequently seen in Pixar films, is the highest rated American actor.
• Arsinée Khanjian was the best actress
• Chuck Norris and Jennifer Love Hewitt won worst actor and worst actress respectively
• Mike Leigh with a rating of 92.1% is the best director. Dennis Dugan was the worst
• Dakota Fanning was the most improved actress

The article has a lot more. Slate also has an interactive tool where you can compare the careers of any major actor or director since 1985.

Source: Slate