Pete Abila, a lean Six Sigma and operational improvement guy who writes a blog, received an email solicitation from Qwest to take a Net Promoter survey and had a few observations about how the invitation was organized, worded and who it was from. He also includes screen shots of the survey itself.
It's a pretty good example of a darned good attempt that just barely misses the mark.
You can see his blog post here: Shmula.com