So, it seems that it's out there! "Who River Song Is" is no longer a secret to those who know where to look. And if you don't know where to look then the 'Doctor Who Spoiler Site' is a great place to start - Only click THIS LINK if you REALLY want to know who she is - I will not be held responsible for you spoiling it for yourselves... You will only have yourself to blame! And it's a BIG spoiler, so don't click it unless you are really, really sure you want to know who River Song actually is! There is doubt among some - and initially, from me - as to whether this spoiler was genuine or not, but since talking to the source myself I'm pretty convinced it is true. And when you think about it, it makes sense!
Right. If you've seen the spoiler there's a chance that you want to discuss it. I implore you not to do so in any form of public place. Blowing the secret on your Twitter feed is low. There are people out there who really don't want to know, who want to find out when the reveal happens on-screen. So be kind, be thoughtful and please don't spoil it for those who want to remain unspoiled. If you want to talk it over with other spoiler-hounds then you can do so on Gallifrey Base's Spoiler and Speculation thread using the link in the sidebar.
But, wow. What a revelation, eh?!