Does anyone have any input on the best ways to gather user profile
information online?  I would like to learn more about who is using our site,
what their interests are, and what type of content they find most valuable,
but I'm concerned that lengthy registration forms will turn new users away.

Most of the content is free, but some requires payment.  So I'd like to have
two levels of registration - if they're signing up as members or purchasing
content, we can ask them a few profile questions as part of the registration
process.  But if they're using free content, how acceptable would it be to
take them through a page of 3-4 questions before first time access?

As an alternative, if we simply provide a "tell us about yourself" link on
our site, will enough people take the time to answer our questions
voluntarily?  And how many questions are "too many?"

Thanks for your input,

Vicky Morville, User Interface Designer