Despite yesterdays reports that the Doctor announces in the new series of The Sarah Jane Adventures that he has an unlimited amount of regenerations, a supposed extract from the script has come to light which, as some other sources claimed, puts a limit on it of 507. The extract is as follows...
Clyde: So, can you like, change colour?
The Doctor: Yes, of course.
Clyde: And how many times can you do it?
The Doctor: 507.
Whether this is made up is unknown, and I think more and more theories will come out until the actual episode airs, but it is another possibility to throw in to the mix