Ask HN: Do AJAX enabled User Registration pages increase conversions?

I am in the middle of creating a new site/business which will ask all users to register an account as well as submit their credit card for payment of the service. Right now I am working on my user registration page. For me this is the most overwhelming part because there are so many things you have to validate as well as getting the credit card info processed correctly. Currently all the validation/processing is done on the back-end once the user clicks "Submit". If there is a validation or processing error, the registration form is displayed again. After polling a few friends on the matter, I was told that I should not repopulate the password or credit card info (number, cvv, billing zip) on the page because this would probably breach a lot of security stuff and possible PCI regulations. I agree they shouldn't be repopulated. But, this presents a rough user experience, because if they goof one thing (email confirmation, for example) they end up having to fill in a lot of the form over again. I also heard suggestions to use AJAX to do some validation work on the front-end before really sending the info to the back-end for final processing. To me, this adds another level of complexity and another point of failure to the system; however this seems to be a much nicer user experience because validation errors are found quicker/easier and they can be corrected before final submission. So, my question is (finally): For those that have gone through this process, what is your recommendation? Does adding AJAX validation substantially raise registration/conversion rates?