I've only used PS3 Media Server a few times but it's worked well for my limited needs, and I've even used it with Remote Play (for Mac-to-PS3-to-PSP streaming) with good results. Haven't tried HD video too much, though.
Also, my understanding is that you won't be able to stream music to the PS3 during a game because it can only play MP3s stored on the PS3 hard drive (for the games that support custom soundtracks).