Consequences of a Solution to NP Complete Problems?

m00nshyn3 asks: "If a person were to find a O(n) solution to an NP complete problem, it would obviously be a great advance in computer science, but what are the consequences of such a discovery? Would our most popular implementations of cryptography be useless overnight? It seems like there is a lot of immediate damage that could occur if such a solution were found. So if (when) the time comes, what is the responsible way for the solution to be made public?" If you had such an algorithm in hand, what could you do with it? It would be interesting to see how many problems we could map into the NP Complete model.