No. Oh God, no. No, no, no. Nein. Nyet. Non. Huh-uh. Negative. I'll qualify that. Extra credit that's built into the syllabus from day one, available to all students equally and in advance, can be defensible. I'd worry if it counted for very much -- a course grade should ultimately reflect performance on the core of the course, rather than the periphery -- but I can see an argument for moving a B to a B-plus in an art history class if the student does (and documents) some museum trips, say.