Dropbox possibly doesn't encrypt user's data but 1Password does. You already have to have two layers of passwords to even get to the encrypted list of passwords stored before hand.

On the shared passwords, I haven't found much use for that ever. Generally speaking, I would just have people create their own accounts or some services allow for sub-user accounts. I can't imagine many use cases having to give someone your password and I'd imagine that the of use of the service is focused on the primary user so whoever they choose to share their password with will have to find their own way to remember the password.

On the note regarding the plugin support, that still doesn't change it's web-base. As for desktop app, unless its a true local machine service, if you're calling back to a server somewhere, it doesn't change the security issues raised in my original post or that of others here.