It's right there in the post:

I gave a brief description of what the website/service offering would be then asked the users:

   Gender
   Age
   Would they use the service as described above
   Give me 3 examples of how they would use the service.
   General feedback or ideas on the service, why they would or would not use it.*

Me, too. I checked my stats after using MT for a site-survey. Most of the users were from the same geographical region, they gave very positive feedback, and they spent very little time on the site. Pair that with an understanding that MT only pays well if you do lots of little tasks very fast, and you start to get the idea that the feedback might not be the most useful.

You need to put in a text box: "Please describe, in your own words, the purpose of my site:" Then throw out all the responses that are incomplete or way off. The problem is that when I did that, there were too few useable results.

This is incredibly good advice. All MTurk tasks of a small size or that will be approved by a single person, should ask an open ended question, that requires a response.

This greatly reduces fraud, and shoddy work. And it has a tendency to highlight the really good workers (some of which are amazing!) - maximizing your benefit as a requester.

or whether people in the target market were remotely likely to be found answering questions on Amazon Mechanical Turk...