At $8, I thought it was worth a punt and decided to sign up. Alas, I cannot complete the process as it gives me an error each time I try to submit the payment information.
So, I ran into this problem -- found out that you have to have the same password on the developer center as you do for your Windows LIVE account. If you have a more secure (or just different) password on the former (e.g. because you have a grandfathered Hotmail account) then you need to change both to be the same to finish the registration process. I suspect that there's some hokeyness in the back-end where the developer center logs in to your Windows LIVE account to mangle something or other.
Not sure that'd be accurate for me since I logged into the dev center using the live account I have (non-hotmail).