If you do a poll from this site its not quite valid no, a lot of the posters we see on here are far more hardcore than the majority who run LFR. Still its useful in one sense as it gives us some data and that's better than no data!
I would love it if blizzard did an in game survey that comes up after the first LFR of the week or something that you do. Just a quick how did you rate the experience out of 5 etc and a small comments box. you could choose to skip it or fill it in. might be something useful to help them get an actual idea of what these players doing the content think of the content.