How data is collected is also very important from both a data validity p.o.v. and a user experience p.o.v.

Data Validity:
Inviting people to participate in surveys via ads as described above is subject to significant bias. Reference Dave Morgan's article “Outing the Heavy Clicker” on Mediapost which, among other things, states…
“Who are these “heavy clickers”? They are predominantly female, indexing at a rate almost double the male population. They are older. They are predominantly Midwesterners, with some concentrations in Mid-Atlantic States and in New England. What kinds of content do they like to view when they are on the Web? Not surprisingly, they look at sweepstakes far more than any other kind of content. Yes, these are the same people that tend to open direct mail and love to talk to telemarketers.”

Polls that are elegantly integrated into a site, like those offered by Vizu's Power-Polls service, can “train” visitors to participate over time by featuring interesting, contextually relevant polls. As a result, they can generate much broader and higher participation rates than invitations to participate in surveys. The improved participation, in turn, can lead to higher quality data about site visitors.

All sections of your site are not equal. To really understand your audience, you may need to understand whether or not different demographics frequent different sections of your site. At Vizu, we have seen sites that have drastically different types of visitors on different sections of the site. Consequently, we designed our Power-Polls service to be able to assess demographics on various sections of a site separately and then roll all of the data into a top level view.

User Experience:
People love polls and generally are not big fans of surveys. Having worked with 1000's of web publishers at Vizu, one of the concerns we heard loud and clear was that of maintaining a high quality visitor experience. Most publishers did not feel that taking their visitors off site to complete a lengthy survey for which there was no reward fit their conception of a positive user experience. On the other hand, many sites get very positive responses from their regular visitors regarding the addition of high quality polling content that offers the opportunity for instantaneous self expression and self assessment. Additionally, given the low click through rates for ads, many sites are not keen on allocating a lot of valuable real estate and impressions to solicitations to take surveys.

Ease of Use:
If you are going to go through the trouble to paste some code on your site to gather visitor demographics, why not paste some code that does more than just that solicit visitors to take a demographic survey? A good polling platform will help you engage your visitors and can improve your site experience. Sites can even opt into professionally produced, contextually relevant polls or rotate in your own polls which you can use as the basis for additional content.

All this is not to say that surveys do not have their place, it just depends what your over all objectives are.

Here is the crux of the issue – In order to do a survey, engage customers, collect data and then analyze and more importantly react to that data – the level of sophistication you need is _much_ more than say putting a feedburner email widget on your blog or putting ad-sense on your blog.

We've tried integration with Ad-Servers and the ultimate bottom-line is that advertisers believe that behavioral and contextual targeting is actually better than “stated choice” targeting. What we are doing (above) with surveys is essentially stated choice targeting.