I am involved in a very exiting innovating service. It is www.seetoo.com.
We make our users share their media contents with their friends instantly, skipping the lengthy file upload phase. We provide synchronized watching experience for the Initiator (broadcaster) and the Viewers (friends). And furthermore - the file size is unlimited, you can run any size you like!
The Initiator have to go through short setup, while the Viewer just should have a Flash player in his browser (same for the Initiator). We support almost every known media formats.
The trick is online media transcoding and streaming from the desktop to SeeToo servers. The synchronization is achieved by constantly monitoring and feedback of all participants and adjusting both the up-going and the down-going streams to the feedback parameters.
We are in operational beta state. All core functionalities are on and working. We are currently working on further enriching the functionality scope.
I would appreciate any your remarks, comments or hints.