My $0.02 about this change.
Users make mistakes, like signing on from an unknown insecure machine. So no matter how secure the password database is, some percentage of users are going to be hacked. Encouraging users to use credentials to an account that has sensitive personal information in order to perform everyday non-sensitive business is going to magnify the severity of the consequences when they are hacked.
So my recommendation for most folks that already has a Ubuntu One account would be to *not* use it for forum access. Create a new account that has as little personal information as possible!
Personally, I came very close to turning my back and walking away from Ubuntu. I'm still wavering a bit. I'm only here to support users of my OSS project. You are on the verge of chasing me away.