Of course the big oil spill is very bad--for the wildlife, for the people, and we still don't know the worst. It already looks bigger than the Exxon Valdez.
What long-term harm did the Exxon Valdez do? I believe there is at least some controversy about that. Here is a paper that may not have been published in a peer-reviewed journal, but it seems pretty reputable. Of course, because it says the long-term damage wasn't bad, it was picked up by the Petroleum Institute.
Wiens, J. A., E. L. Brannon, J. Burns, D. L. Garshelis, A. A. Hoover-Miller, R. H. Day, C. B. Johnson,
and S. M. Murphy. 1999. Fish and wildlife recovery following the Exxon Valdez oil spill. Pp.
127– 133 in Proceedings of the 1999 International Oil Spill Conference, Seattle, Washington.
Publication No. 4686B, American Petroleum Institute, Washington, DC.