So Wim has been hacking on with the GStreamer RTP support and we have managed to play all our internal streams correctly now testing with the Darwin Quicktime Server, Axis RTP network camera and the RTP branch of Flumotion. There are still a few cosmetic things not working perfectly like getting Totem to display the name of the codecs being used, but all in all things are looking very sweet.
So if you want to help us out make it truly robust we ask that people grab latest CVS of GStreamer and the plugins modules and try to test out using Totem and playbin against local and internet RTP streams they have access too. GStreamer contains depayloaders for most MPEG/3GPP related payload types and Fluendo will soon add Windows Media RTP support to our codec package. The only major RTP (or rather RTP like) thing not supported yet is Real media and also Apple RTP of their older proprietary formats (Sorenson/QDM2). And of course we support Vorbis, Speex and Theora RTP streams :)
I made a claim that sync was solved in current CVS and this turned out to be wrong and based on some miscommunication. Sync is still not fully done and it will still be a few weeks before it is so. According to Wim the only reason sync is better atm is purely coincidental. Testers are still very welcome though as it would allow us to sort out issues such as server compatability and so on.
After some lunchtime discussion it turned out my claim about sync was true afterall. Sync is now perfect for RTSP streams. What is missing is RTCP sync. :)
Also regarding the question of serving RTP there will be some rudimentary support in GStreamer once this work is done. Furthermore there are people from Axis working on enabling GStreamer as a RTP serving system so expect to see further updates on that front.