This seems like one of the most important feature needs to me, as well. I find that I go in bursts "tabbling" stuff, then the interface sits behind my work and I forget to tag. I would love the ability to right-click a file in explorer and reach Tabbles features: both to tag and to invoke a search.
Usability-wise, the tagging would need to allow multiple categories to be selected in the single operation. What I mean is that having to right-click and choose each Tabble to associate with a file would be very cumbersome. A persistant function that allows one to select multiple tabbles during the tagging operation would be slick.
Thanks for being so responsive, by the way!