Inspired by the fantastic new Audi VDT site produced by ArtificialDuck using Away3d, I decided to go on a little exploratory tour of the current Away3d codebase to see what could be done about fast(er) rendered 3d particles.
My results use a new set of classes soon to be uploaded to the trunk in the 2.2.6 dot release of Away3d – basically with this update it will be possible to create single 3d objects containing many particles, greatly reducing the number of matrix calculations required for rendering a collection of particle objects (or billboards as they’re more commonly known).
The above test is a bit of an extreme case so may run slow on older machines – 4096 stars are being rendered independently per frame, with a bit of mouse-influenced movement nicked from the Audi site 
The classes have yet to be properly optimised, but I hope to be able to provide full source soon along with an update to the Away3d trunk once things are complete. In the meantime the demo has a bit of a festive look, so seemed fitting to release over the winter break. Hope you like and merry christmas!
*Update*
Source is now available for the demo above via the usual right-click menu or this direct link. You will require the latest trunk version of Away3d from the svn, version 2.2.6. On a side note, the default demo now renders 1024 stars to get a smoother framerate. With this number of billboards, things fly!