How long?

[4thDoctor]

How long do you think that an actor should remain in the role of the Doctor before being replaced? Tom Baker still holds the record of seven years in the part, should anyone attempt to break his record?

[Nolamom]

I don't think it's a question of setting a record. It's more a question of how well received he is in the role, how comfortable he is in playing the role, and whether or not continuing with the same actor is in the best interests of the franchise.

[Pharaoh Atem]

the actor that plays the Doctor should stay on as long as he (or someday maybe) she is happy and still enjoying the series.

[Quizziard]

And as long as they are being given good scripts, budget and directors (etc.)

[Cold Fuzz]

Christopher Eccleston's stay as the Ninth Doctor was too short for me but I understand his decision to leave. I thought David Tennant stayed way too long for my taste. By the time we got to Voyage of the Damned I wanted somebody else.

Matt Smith on the other hand is doing just fine I think. If the Silence aren't vanquished at the end of series 6 and it keeps going into next year then I get the feeling that when the Silence finally goes, so will Matt Smith.