(No I'm not a pirate)
I've been working on computers for a rather long time and personally myself nor any of my associates have come across this issue. However, on my personal computer that I recently finished building was on a seesaw back and forth between internet and no internet. As of late Ive been getting this issue more and more.
After an hour and twenty minute phone call running through tech advice from the clowns at Microsoft they left with no answer or resolution in sight. This issue that is happening currently is that Im connected through a Linksys Wireless G router and Im wired to it. Other devices such as the the computer Im typing still manages to get online along with my Xbox 360 wired as well.
Ive run all the hotfixes and still nothing.