Session 0 and 1 in Vista
Earlier today a colleague asked how do Services and Applications talk to each other in Vista and I said, "the way they used to earlier". I wasn't aware of Session 0 and Session 1 concept till now. He pointed me to this MSDN article that explains what this new concept of Session 0 in Vista is all about.
This essentially is to prevent direct access to services from applications and thus prevent hacker to elevate their own security priviledges. Some information around this is here and on this Channel 9 video. A white paper on impact of session 0 on services and drivers is also available.
[Edited April 16, 2007] Found some tips to communicating with Session 0 services here.