In reply to mark k..

The problem is that OAuth is not designed for something intended to be distributed to users. Basically, to use it, you have to have two web services talking to each other using an account from a third party. It's poorly designed for use by WordPress plugins, really, because in such a case, there's no third party. In order to use it effectively, the plugin author has to create and host a separate web service just for relaying authentication credentials around, in order to preserve the "secret" part of the authentication system. Badly designed, basically.

Storing usernames and passwords is bad, but having to relay all authentication and quite a lot of the messaging through a third-party do-nothing web service isn't much better, honestly.