On my iPad, dowload is too slow to stay aheaad of the stream, thus it pauses, both in safari and the youtube app.
Connecting thru a new Airport Express on N. Measured speed with the app posted earlier 3 times with results from 7.5mbps to 14mbps.
Same video on my Verizon Touch Pro 2 connected via G on Linksys wrt120n does not pause at all, and the download appears to be about 2.5x the playing speed.
So those results are in conflict. An N connection thru a new router with a high measured speed stutters on the iPad, but not on a good G connection on a phone, thru same cablemodem.
For a quick comparison, I was able to stream VevoHD and Netflix with no problems on the iPad thru the same connection.