I hate to post bad news and I don't really like to speculate about game releases, but according to steampowered.com, the release date of S.T.A.L.K.E.R.: Clear Sky has been delayed by one week.
I'm not sure if the retail version of the game will be delayed, but as far as Steam is concerned, you won't be able to get the game from Steam until September 5th. This is very bad news for all of us fans of Clear Sky. I know one week is not really a lot of time, but when you're impatient about the release of a game, well one week is like...forever.
The reliability of the source is high and personally I don't think this is a bug with the game's profile on Steam. And there are also some rumors that the release has been pushed back one week on Amazon as well. There's still no official word from Deep Silver about this matter, as soon as they confirm whether this is true, I'll let you know.
Anyways, let's be positive and consider this news from another perspective. Deadlines are usually very annoying for any developer and today's tendency is to sacrifice "polishing" to meet the deadlines. If Deep Silver has just found a bug on the game and they need to push back the release date by one week, that's fine.
UPDATE: Deep Silver has confirmed that Clear Sky has been delayed until September 5th for both retail and Steam versions.