What percentage of people who click on your "sign up" or "create an account" button actually fill out and submit the form?
Note that I am NOT asking how many people who come to your site click on the "signup" or "create an account" button (but if you want to answer that question, too, I think it would be interesting)
Moreover, anything you can do to reduce the number of steps and requirements for the user will also improve conversion. For example, does your product really need them to confirm their password if they can have it emailed to them when they sign up or at any future time? Try removing unnecessary form fields, or deferring them until after the user has signed up.
For reference, my most recent site (still in development) has the sign-up form on the front page, and we're able to convert 10-15% of random visitors from AdWords. I feel like that's pretty good. On another site, I struggled to get 8-10% overall conversion. And, on a very simple project (http://file.io) that received a good number of hits from del.icio.us/popular (very targeted/interested traffic), I was converting greater than 25%.
Just keep making it simpler, and keep testing, and you can improve your page.