That depends, I managed quite well when I used TVersity, anything that is compressed a bit works fine, 10mbps is no problem, I guess streaming double layered BluRay's doesn't work so well.
Now I don't use streaming anymore, my PC isn't on normally and whenever I want to watch a movie I just use a 160GB external drive, if the file needs to be split due to the 4GB limit I use mkv2vob (which I use anyway as it guarantees the PS3 can play the file)