From my experience they were good.. Kept communication up, although I'm pretty sure they replied from the US as they replied at odd times. Turn around was maybe 2 weeks from them getting it to me receiving the goods back.
I have nothing but good things to say about my dealings with Corsair, twice I've had to contact them due to issues with my 800D.
First off, my wife was hoovering and decided to try and move the case by pulling the door... in a shocking turn of events that nobody could possibly have seen coming the tiny little plastic hinges on the door snapped and the door fell off. I contacted Corsair to enquire about the possibility of purchasing a new door, and they were kind enough to ship me one, completely for free, they didnt even ask me to pay the postage.
The other mistake was I broke one of the hotswap HD bays... computer maintanence after several beers isnt the best idea. Again I contact them via email and they sent me out 2 bays the next day, one to replace the broken one and a spare incase I was stupid again.
Must admit, I didnt get a reply within 24 hours either, but given the nature of the resolutions I got from them I wont begrudge them that.
I posted on their forums when my 550W PSU was failing and got an almost instant response with details on where to send it. The rep from the forums gives you a code to include from what I remember, kind of like an "I sent him, it's okay" code I think?