A lot of the backend code for tagging has been added quite awhile ago, but it seems to have stalled (before I came around). I do believe it's on the schedule to come out in a near-future release, but the development team has been focusing on fixing bugs, etc. before diving in to see where the tagging code was left off.
Thanks for the quick response. I found the latest branch with tagging and I'm going to try to finish it for a project I'm working on. If I do, I'll post.
The last branch that works with tagging was 2.1, while the latest released version is 3.0. You might take a look at the latest SVN code (rev572) and see if you can implement the old tagging code in this latest version, rather than working with an outdated version of Plogger.