Lately I've been having issues with Netflix on my 360.  Sometimes I get HD with full bars.  Sometimes I get no HD but something like 4-5 bars.  Sometimes I only have 1 bar.  What's worse is it will vary while I'm watching whatever I'm wathing. 

I have my 360 hooked up via the ethernet port and I've tried several different cables and have tried at many different times of the day and night and I'm getting the same results.  I would say perhaps it's my internet connection or Netflix is busy but it runs fine on my PC and PS3 with no problems whatsoever.

I've looked around and it seems other people have had these problems but I haven't seen how to fix them.

When I had Netflix I had this problem and was told it's my internet connection speed fluctuating.

All I could find was a possible port problem. Here is a link to info on it : http://support.microsoft.com/kb/908874

I don't know if that is the problem, but looks like you can test it on your xbox.