Well, it means that it doesn't work. It has been major subject of laugher and cry in Helsinki. Even if you have 10Gbit/s connection, it's "too slow" for streaming youtube videos (at any resolution) reliably. Yep, unfortunate but true. "Too slow" in this case means that the bottleneck is some where else in the network, but it still means that it simply doesn't work properly.

Any ideas where the bottleneck is? Is this a latency issue? What is your ping to s.ytimg.com like?