We had purchased a Roku XD|S and set it up yesterday. Everything seemed fine until we wanted to watch HD content. Everything under Netflix that has HD content (Lost Seasons, for example) would only play in SD. Free TV episodes under Amazon VOD would be spotty, sometimes loading as HD during buffering...other times switching back to SD when it had to rebuffer.
I decided to implement the settings in FurryNutz's Xbox sticky, assigning a static IP for the Roku and applying the gamefuel settings as well. Still, the issues with HD persisted. I even tried the hidden bandwidth setting of the Roku (press Home 5 times, Rewind 3 times and FastForward 2 times) to fool around with debug mode and later, applying bandwidth settings anywhere from 1.5Mbps to x3.5Mbps. The Roku settings helped, but buffering times went from 20-30 seconds to literally 5+ minutes.
So, I left it until this morning to retry, just in case it was related to Comcast cable and possible heavy neighboring traffic (due to the blizzard in our area). Still no HD. So, it was time to do a little more router and Roku editing.
We were running the router on a combo 802.11g and n, at 2.4GHz. I switched this to 802.11n only at 5GHz. I then edited the Roku's hidden bandwidth setting to x3.5. Voila! Every single HD video now loads (and stays) in HD, without the extremely long buffer time from yesterday's settings. It works great in Netflix, Amazon VOD, Vimeo and other channels.
I'll keep testing to make sure it keeps working this way, but I wanted to post this in case others experience similar issues with a Roku and the DGL-4500.