If you pre-order from Steam, you will receive some Team Fortress 2 items related to The Cave.
No release date has been officially announced, but according to MyXboxLive, The Cave is now up on the Xbox Live Marketplace with a release date set for the 23rd of January. The size of the download is 1010.70 MB according to a tweet by Greg Rice.
Update: The January 23rd release date has now been confirmed by Ron Gilbert on twitter for Steam and XBLA. It will release one day earlier, on January 22, for PSN and Wii U. It's also coming to Mac and Linux through Steam as well as Windows.