Update 2: As the demo-induced BioShock frenzy continues, 2K community manager Elizabeth Tobey has announced the release of a free downloadable BioShock art book. The PDF-format book is print-ready.
Update: 2K Games has announced that the PC demo of BioShock is "in its final stages of testing and approval," and is planned to be released this month. The company did not definitively announce whether the demo will be released before the game's August 21 release date, but an announcement is expected soon.
Original story: Following the announcement that a BioShock-related announcement would be announced tonight on SpikeTV, journo Geoff Keighley announced availability of an Xbox 360 demo now downloadable via Xbox Live. Publisher 2K Games followed the announcement with its own announcement on The Cult of Rapture, the company's site dedicated to the game.
Many users attempting to download the demo have announced unusually slow download speeds, suggesting Xbox Live is being heavily taxed by the demand.
Along with the announcement of the Xbox 360 demo, Cult of Rapture overlord (and Shacker) Elizabeth Tobey announced a PC version of the demo will be released "later this month." Further announcements regarding a PC demo will be announced tomorrow, Tobey announced. BioShock ships next week.
In related news, Shacknews Ltd. today announced its intention to cover any further announcements regarding BioShock demos or announcements regarding announcements related to BioShock demos.