A thread on the Steam forums seems to confirm that rumours about a new Counter-Strike game – Counter-Strike: Global Offensive – are true, with commenter “Cliffe” (who is Valve designer chap Jess Cliffe) saying “Global Offensive”. There have been a bunch of other references to it, on Twitter and so forth.
And update on the ESEA Facebook page reads “Counter-Strike: Global Offensive… More info in the morning.” So it looks like we can expect something later today.
We'll have to wait for more information, but I'll try to update this news post when we hear anything.
[Update] The game now has an official page on the Steam store, giving a few more details.
And, thanks to MaK, the official trailer: