We are thinking about signing up for FormsCentral to do a contest (among potentially other things). One important feature to us is that people are only allowed to submit the form one time. Does FormsCentral have the ability to do this? Thanks!
No, limiting submissions from one user is not something FormsCentral supports.
You can embed the from into your own web page that you could control access to where you set up a system only allowing users to log into that page one time, when the user submits the form it could redirect out of that page and then the user would not be able to log into it to fill out the form again. But this would all (except the redirect) be controlled by you and your website.