Polls are the logical entry for any social network due to their simplicity to implement. Further, any more thorough true market research provides a much higher level of maintenance and sales cycle between the audience/respondent and research professional. This is in part due to the historical high use of incentives for market research and as a result, becomes an administrative nightmare.
Polls are single questions, no logic, and little burden for the respondent - thus no real value proposition is needed. I would argue that if you get people at the right time, there is an incentive for respondents to provide insights beyond a simple poll. We just need to get outside of the 'email panel' or 'registrant' way of thinking. More to come on this . . .