Just hooked up Roku HD (the cheapest one) yesterday using wireless connection. I have an old TV with one co-ax input so I am using a VCR for the Roku and the HD converter I have to connect to the TV. I have composite video cables connecting the Roku to the VCR and a coax cable from the VCR to the TV. The wireless signal strength is "excellent" and the picture quality I see 4 dots (I assume this is the 4 dots I see when the program is "retrieving"). My issue is that the picture quality is very poor. The picture typically starts good, but gets very dark and there are lines that will roll up the screen. And it will gradually get better, look good for maybe 10 seconds and cycle through the same state. I have played a couple different episodes of different shows with the same problem. Sound quality is not affected.
Crackle worked perfectly.
I have verified that the cables are attached tightly and have moved them around with no changes.