If you are currently using Pintera to access Pinterest then make sure you do not log out. If you are already logged in, anything you do that requires a login will still work. Once logged out you cannot log back in right now.
Since this affects all the Pinterest apps the same, they are all getting poor reviews from new users (not unexpected when the app doesn’t do anything useful). Given that fact, I have decided to hide the application on the marketplace for now. It will still be available and will still function for you who already have it. It will just not show up in searches so that new users will not find it and get a bad first impression.
If you need to get to the marketplace page for it you can go directly to http://www.windowsphone.com/en-US/apps/e90ec640-dcff-4586-9d8f-2fc552b3f4d5. As soon as this gets resolved I will open it back up to the general public.