Possible Duplicate:
Do you lose the points you acquired from a question if/when is deleted?
While I agree with the general principle of downvotes costing reputation, I think there are cases where there should be a refund, or even a gain in reputation.
The main example is the case where an answer is downvoted because it was wrong or misleading, that answer's author acknowledges this, and deletes their answer (maybe because there is already a suitable answer).
Given that reputation is supposed to recognise your knowledge and, er, reputation, I think that it seems wrong that you loose reputation for highlighting a mistake that is later acknowledged.