Gstreamer as installed on the Pre is version 0.10.21, along with a patch. The patch seems to do minor error handling, along with registry adjustment. The registry in Gstreamer is used to "install" new plugins that are added to the library (plugins are generally located in /usr/lib/gstreamer-0.10/). As of Gstreamer version 0.10, this is an automated service, no user entry is neccesary to update plugins. In fact, each time "gst-inspect" is ran, plugins should update automatically. For an unknown reason, Palm has decided to edit it in such a way that this is no longer the case. One theory is that Palm-built plugins were not registering correctly, so they adjusted the mechanism of the gst registry. Work is currently underway (by ajames) to either edit the existing system, or create an alternate work around. This should allow developers to build and "install" plugins (and elements within) that are compatible with gstreamer.
Once the community gets a working gstreamer plugin environment, it opens up many possibilities, including alternative audio and video filetype support (encoding and decoding), as well as video and audio streaming with the Pre as the source (icecast, etc). It should even be possible to create an app to encode or recode various types of audio/video files into other formats, right on your phone.
Additional information can be found at the VideoRecording wiki page.