It really depends on how obscure you thing this issue is.

I would advise the search company/s of the issue and wait for a response.

After a reasonable amount of time (your decision) I would publish.

Since this is not a security issue but a search problem I don't see hackers going wild with it. I mean how much fun is Beavis going to have trying to mess up IBM's page rank?

__________________
"The future is here. It's just not evenly distributed.