Well, I don't know if this will help you or not, but I can give you my findings using wireless so far.
I started out on a d-link DI 514 wireless router. it only supports up to B. when I first got my box, The first day I was getting 4 dot quality mostly and did see a 3 and a 2 once. After that day, it was always a 1 or 2 dot quality. I went into debug mode and forced it to 4 dot quality (2.2meg) and it would start it in 4 dot quality every time. I would end up buffering a movie anywhere from 1-3 times during a 1.5 hour movie. It was kind of a pain but at least I was getting the best quality. BTW, I did check all my router settings and they were set correctly.
Well, I went out and bought a d-link DIR 655 wireless N router. I force the router to G and N only. Took out the forced video quality of 4 and tried it. First few movies I watched was 4 dot quality then it started to go down to 3 or even 2 dot quality. In watching the signal from the administrators page on the router, the signal quality was anywhere from 30% to 80% randomly. Bitrate fluctuated a heck of a lot more. I saw it as high as 36 and as low as 5.6.
So in troubleshooting, I did the following. The modem is still in the same position it was in before but I went into the roku box and forced 4 dot quality again. I have run that for 3 days and every single movie has played flawlessly. Not one time has it tried to re-buffer and that is watching over 15 movies in the last 3 days. It simply plays great at 4 dot setting and nothing has changed with the position of my router. If I set it back to autodetect, and turn on debug feedback, Most of the time it will give me 2-3 dot quality and tell me that my network is only 1.9 meg or 2.1 meg even though it can do 54 meg. Yet if I force it to always do 4 dot quality it works flawlessly with no re-buffering.
So I did yet another experiment. I played with the positioning of my router to the roku box. Currently the router goes through 2 closets and 2 walls to get to the roku box. I took the router and placed it in the center of the house (only a partial wall in the way) and then went back and watched the admin page on the router. steady 54 meg connection to the roku box. Level 4 quality every time without forcing it. Another side note, My internet connection is 10Mb down and 512 up (stupid time warner and their stupidly slow upload speeds)
So to conclude, wireless is flaky at best, and to prove that, I have another laptop that sets about 6 feet away from the router and maintains a 100 signal all the time yet the bitrate will fluctuate from 54 down to around 11. It shouldnt but hey, its wireless Oh as a side note, there are no other routers around where I live for at least a mile so interference from another router is not a problem . If you don't have a line of sight with the roku and your wireless router, dont expect it to give you the best quality. Your only options (that I can think of are:)
1. Force the roku box to always do 4 quality
2. move your router to get a better signal to your roku box
3. Go for a bridge or signal booster
4. go wired.
I for one at some point may move my router but that means stringing a bunch of 25 foot ethernet cables around and that I don't really want to do. So as long as the roku box will allow me to force the video quality I want, I may be content with keeping things like they are. If they take that ability away, it may force me to either buy a bridge and install it or actually run a wired line all the way to my router. Neither of which I want to actually do but I dont think I can accept what the roku THINKS is my wireless as in my case it is not accurate.