Really curious to see if there are other Roku users who are experiencing the same problem.
Count me among those with this problem. I can stream Netflix and Amazon VOD perfectly fine on my Vizio connected set, but the Roku XD that I just got refuses to stream HD even though my download speed exceeds 15Mbps and my wireless connection reads excellent when I do a network test. I even ran a test with both the TV and the Roku streaming simultaneously. The TV ran HD just fine and never re-buffered; the Roku dropped down to SD and re-buffered often.
I spoke with Roku tech support and after redoing all the diagnostic work I had already done, they suggested I change my DNS server to OpenDNS. I don't think this helped, but it didn't hurt anything, so I have left it this way.
Any suggestions from the experts?