I think it came out in Europe already. I don't know for sure though.
No, it hasn't. Hence why we know so little about it, and the only videos of it are when people got to see it for the first time at CTIA 2010 in March.
The problem with guessing a release date here is that we don't know when the device will release on different carriers.
Just because Samsung decides to release the device on a certain day doesn't mean the carriers will.
We can probably assume that AT&T will have the device first as we've already seen a model for them come through the FCC. However, they don't seem to have much love for Android devices (just look at how they neutered the Backflip) so I'm not too sure they'll rush the Galaxy S out onto the market, particularly if they're starting to focus on the iPhone 4 for release this summer. And I sincerely hope they don't do anything stupid to the Galaxy S either.
T-Mobile will probably be next, if not right around the same time. T-Mobile has been doing an excellent job of picking up powerful smartphones in recent history in order to expand their user base. They don't have the most impressive network, but they've got a good lineup of phones.
Sprint is busy showering the EVO 4G with limelight and touting their (small) 4G network. I can't see them pushing the Galaxy S when they're aggressively marketing the EVO 4G.
Verizon is supposed to be the last one to get the Galaxy S. I suppose it makes sense, they'll probably release later this Fall after the hubbub over the HTC Incredible has died down. Windows Mobile 7 Series phones will be starting to come out around that time, and a new flagship Android device will be due as well.
The problem is, most everyone is pushing a high-end smartphone right now. T-Mobile is still pushing the HD2, which was released in November and is already starting to show it's age, particularly with Windows Mobile 6.5 squelching sales, and the EVO 4G overshadowing it. I could see them actually putting some advertising into the Galaxy S.
So... we'll see. I'm just wondering if any of the other US carriers plan on switching gears to market the Galaxy S, or if this is going to be a phone that just quietly appears on the shelf...