The Intelligence firms are going to get the information they want regardless of what services you avoid, if everyone abandoned Yahoo then the intelligence forces would just get the information from the service that everyone switched to instead, I think the real solution is to demand that the Government stop spying on people.
When we purchase a computer and a webcam, we are not informed that at any time we are going to be watched and monitored by our government. Even if we are not criminals, and we are not doing anything wrong, that doesn't mean that our privacy is sacred to us.
I stopped using all of Yahoo! services a few years ago after my e-mail account was hacked and the password was stolen. After this happen I changed to a different provider and haven't looked back once. Yahoo! has some serious security issues, but I'm sure they share these problems with all providers. These spying problems won't be resolved until the citizens stand up against them.
I will not use Yahoo! webcam services knowing that my information and even my image can be tracked by UK intelligence firms. I think that it is a total breach of trust for such a thing to exist. The risk would just not be worth it. I do not see how anybody could risk it.