Great article. I have found...and tend to think, in a lot of cases, that offering the passwords, etc. signifies nothing to hide. Openness. That step alone basically diffuses the need to check or utilize the passwords. The knowing that if was needed..you can. And that your partner is okay with that.
Not sure about boyfriend/girlfriend dynamics(depends on long term potential) but I certainly don't think it's an unwise thing to do entering into engagement and/or marriage. That level of trust, transparency and - frankly - sense of accountability impacts a positive climate for genuine intimacy (which requires varying degrees of willing vulnerability & transparency). In spite of what this article states, it is the message of willing vulnerability and transparency that matters here, with, of course, the caveat that the recipient of the passwords understands this and treats that openness with care and respect. The willingness to be that open counts a great deal. It's affect powerful. It also lets your partner know that you truly care about their position of vulnerability in trusting as well...not just your "rights". That, in my opinion, is all part of giving of yourself in a real relationship. Offered, not demanded or imposed. That's the key, here. And in my experience, it goes very far.