Officially, Google has only stated that Chrome OS devices will be arriving late this fall "from select partners." So who might those partners include? If the files I spotted in the Chromium OS Git repository are any indication, Acer, Dell and HP are good bets. The overlay-x86 bits take care of configuring Chrome's hardware support during the build process -- so these would seem to indicate that Dell, Acer, and HP might be at the point where they're building the OS for specific configs.
Apart from the conspicuous files, all three have already been connected to Chrome OS in some way. Dell engineers put together a customized build for their Mini 10V netbook shortly after Google opened the Chromium OS code. As Sebastian wrote recently, HP is tinkering with Cloud Print -- which will feature prominently in Chrome OS. They're also not averse to trying different things with their netbooks -- like their heavily-customized Ubuntu remix.
As for Acer... Well, if anyone's willing to try cramming a Chrome OS dual boot option onto a netbook, it's Acer. They already tried an Android/Windows combo with the AOD250, but that didn't turn out so well.
Acer and HP were, of course, mentioned in Google's initial "so who's working with us on Chrome OS?" post. While Dell was left off the list, I'm not surprised to see their name in the project files. Who better to help sell your OS to consumers than the top 3 OEMs in the game?