Streaming and buffering in SharePoint 2010

The best single link is a fairly new Technet article on caching and performance planning with SharePoint 2010: Summary: performance can be tuned through disk-based BLOB caching and bit rate throttling

Bitrate throttling configuration walkthrough: Summary: detailed guide from the IIS team

More direction on where we’re going with streaming (the out-of the-box media web part uses buffering, NOT streaming. Streaming is enabled via IIS media services): Summary: good overview of IIS Media Services 3.0

And finally, Silverlight 4 capabilities, including multicasting. Currently SL4 is in beta: