Sorry, I didn't mean to be flippant. I was in transit and should've waited to respond fully.
To clarify what I meant previously, this is only a problem for users who have created tags with the same slug as a user's user_login. Pre-3.0, this meant that either the tag or the author term was appended with '-2' or similar. This wasn't a problem pre-3.0 because Co-Authors Plus did the lookup based on term name — now it is a problem because we've switched to term slug.
Based on the number of reports I've gotten thus far, I don't believe this is widespread-enough of a problem to devote development hours to it. In fact, the most significant upgrade issue seemed to be users who modified their user_nicename value — something I didn't even consider to be a potential problem.
To use Co-Authors Plus, a user will already have to be reasonably proficient because they have to edit their theme templates. I can't proactively account for every possible conflict. For this particular problem, I think it's reasonable to offer these forum threads as documentation of the issue and steps that need to be taken in order to fix it.
I only came to help other users of your (quite good) plugin.
I'm very happy to have you around, and I again apologize if I came off harsh. Offering free support for a free plugin is a bit grueling at times. I appreciate any help I can get.