Sorry to say that, but miknos I don't think your problem is the same than our.
We are talking about the computer going black randomly (fans always on) and no other way than hard reboot, followed by a kernel panic.
Alright guys, I've done the clean install, without Wi-Fi. I'm plugged in with ethernet and I never crashed. I will try to enable Wi-Fi to see if I crash now.
Edit : I crashed 2 times with Wi-Fi within 30 minutes I think that the problem is more likely to produce with the Mac App Store because it is checking internet every time. Now I'm going to try ethernet a few hours again.
I'll try to connect to another Wi-Fi network too, because the one I'm using is opened with no SSID broadcasting. Maybe that's the reason. I'll try this after ethernet.
Interesting stuff, keep us updated.