I changed my login ID on my home computer and then I was unable to login on my work computer. Accessing the the login link just gave an error, I was unable to even get to a point where I could type in my new ID (Error Text: HPDIA0114E Could not acquire a client credential.). The solution was to delete my cache/cookies/etc and then I was able to login.
I should partially take back my comment about the new forums being quicker, it takes 20-30 seconds to log in and see the main page which is not great. Navigating to the various forums and messages is maybe a little quicker than the old system though.