Somewhere. I am presuming North American Steam accounts can see it and download it and play it, if they have pre-ordered, due to this post on the main site. The Space Marine page is not visible here in the UK at all. I contacted THQ to ask why that would be quite some time back, but we've yet to get a response. Our guess is that it's related to a retail distribution deal in the UK, but we're just speculating. Anyway, Relic have announced that signing up to this Honor Guard thing will give UK users access to the demo on August 22nd, somehow. The demo apparently gets a general release on the 23rd, but I am not totally clear about that.
Anyone played it yet? The game is due out September 6th in North America and September 9th in Europe.