There was an article posted on Engadget about how a Microsoft survey hints at an Instant On OS concept.

http://www.engadget.com/2008/10/15/microsoft-survey-hints-at-instant-on-os-concept

Yes the article is about a locally running OS, but I would beg to differ, and say the Instant On OS is here now, and is not a concept!

If you were looking for the ability to have an Instant On Desktop, then all you need is a Thin client, Citrix Desktop Reciever, and Citrix XenDesktop. You would turn on the Thin Client and then you would Logon to your desktop, which would already be on, as it would be in the data center waiting for you to log on.