Designing registration forms is never anyones favorite task, especially for ad-supported social networks. For these situations, it often becomes a dramatic tug of war between interaction designers, usability folk, and ad sales. The interaction designers and usability experts obviously want as simple of a registration flow as possible in order to increase conversion but ad sales would love to add as many form fields as possible. Ad folk usually don't care about the user experience (which really doesn't make too much sense).
But wait. Isn't everyone just trying to get new users acquired?
If you asked someone in advertising they would say something like more users are OK, but what they really need are the demographics of their users in order to target better ads and get a higher click through rate.
All that being said, there are some sites that break the mold: like that of Squarespace. It'd be tough to make this form any easier. As far as blogging platforms go, it's the holy grail of usability and ease of use:
15 seconds! Compare this to any other social networking site, and you'll begin to see what I mean. Some sites even have the audacity to make you confirm your email address before you can sign up. Forget about multiple pages and an unknown number of steps-- we're talking about leaving your session and opening up your email! Why have the possibility for countless leaks in your conversion funnel? It makes no sense!
Although it might be better for advertisers, you have to draw a line between their needs and the needs and user experience of your users. As far as users are concerned, they don't see the reason for knowing what zip code they're in, how old they are, or what their gender is if all they want to do is start a free blog. Remember, happy users are loyal users. And even a smaller number of loyal users will be much more lucrative than a bunch of drop-off users. But my guess is you'll end up having a greater number of happy users if the experience is there.
Of course, what might make users WANT to fill out extra demographic fields would be some kind of incentive. Perhaps a revenue share? If users received a percentage of advertising revenue their site generated, then of course they'd want to do everything in their power to help increase revenue. Otherwise, it's all just more effort for little reward.
