What is the average conversion rate for web sites on their registration screens?

There are lots and lots of sites out there but when a user goes to
click on some information they would like to see and they land on a
registration screen, lots of them do not sign up.  I'm curious to know
what the average number is for users that actually do do the
registration process and sign up as a user.

Depending on the type of website visited and the relevancy to the
user, the chances of having users sign up is very low. As an example,
porn sites often offer webmasters referral money to send people to the
website (and more if the users sign up and become paying subscribers).
In the short run, just sending people to the site generates more
revenue for the webmaster than that of the actual small percentage
that become subscribers. This concept is applied to many other
websites as well (such as online survey sites, etc.).

Hope this helps!

I appreciate the comment.

What about sites that are interactive?  I'm thinking Web 2.0 sites
that involve user interaction to be compelling.  Or, what about
posting a comment on a blog?  Again, you usually have to sign up for
an account.  I'm not looking for the exact number, just curious if
anybody has done some research on this and has some general
percentages.

Again, all answers will be subjective. I could easily say that more
than 80% of viewers eventually sign-up; obviously they're at the site
for a reason. Take MySpace for example: To view someone's pictures,
you have to have an account. Blogging sites, such as Xanga, require
that you have an account to post a comment/reply. Viewers that view
the page and log in aren't considered new sign-ups and I would assume
that most people who are trying to post a comment/reply would already
have an account; those that don't have an account will spend the time
required to set one up.
Clearer? Ask me for more if needed!