Google has just released their “disavow link” tool.
If you're going to use it, use it carefully. Test first. Err on the side of caution.
Personally, I don't intend to use it at all. I understand why people want it but… no.
On a related note – do you have any idea how many ex-friends and ex-clients still have me looped into access to their GWT accounts? Access that I myself can't revoke if I wanted to. If I were an evil person, I could do some *serious* damage.
Time to check who all has access to your GWT. Do it NOW.