Okay, I just did a simple test of what happens when I change my Pandora password. There is a record of HTML local storage keyed on "jStorage" which appears to be a giant JSON blob. A specific attribute whose name appears to be a randomly generated (encrypted) is updated.
Assuming that is password, stored encrypted, the exposure here may not be what people think. It certainly would mean the password need not be stored at all on Pandora's server. They could just have an HMAC. The password value could be simple extracted from local storage. Has anyone checked to see if this is the case?
Follow up: Okay, I further confirmed that if I set the password back to a prior value, that field in jStorage flips back to the prior value. So, it looks like it is stored encrypted, locally on the system. I haven't traced through all the JavaScript, but it seems likely that the security issue here is different than perceived, and might even be non-existant.