Jumping on the NSA/Prism questions bandwagon - There's been a lot more attention drawn to facilities such as [Room 641A](http://en.wikipedia.org/wiki/Room_641A) which indicate that the NSA has been, amongst other things, applying mass intercepts to communications through large US ISPs. 

One thing that strikes me as odd in these techniques is that although they could collect a large amount of unencrypted data, large sites such as Google, Facebook, Twitter and many others typically redirect to HTTPS sites by default. This begs the question - how useful can the unencrypted data be, and do intelligence agencies have a way to decrypt the rest of it?

I know as little about this program as the next guy, but a lot of the descriptions of this program indicate that various intelligence agencies use demands such as [National Security Letters](http://en.wikipedia.org/wiki/National_security_letter) to request information, or make demands such as that on [Verizon](http://www.guardian.co.uk/world/interactive/2013/jun/06/verizon-telephone-data-court-order) to have metadata sent back on a recurring basis. If that's the case, what purpose could monitoring/recording internet traffic serve? 

It's my understanding that, without having broken SSL/TLS the only way to decrypt encrypted traffic would be through having access to either a root certificate, forging a certificate for the domain you want to monitor and running a MITM attack, or through having access to the private key of the domain you want to monitor. 

On the other hand, the NSA are much further ahead in crypto research than any public body, so there could be a possibility they've found a weakness? (Or simply have the compute power to break it through brute force)

Edit 2013-09-06: The Guardian has today published a story that something alarmingly similar to my question is taking place. [Article here](http://www.theguardian.com/world/2013/sep/05/nsa-gchq-encryption-codes-security)