Even better, off load this to a GUI plugin, then people can choose the method that works best for them. But I still like Jonathan's original implementation the best.
While there may be "better," neither of them will be best when one relies on the Tcl/tk's implementation that delivers inconsistent results (which is BTW yet another frustrating form of cognitive load whose scope is significantly larger than either of the ones discussed below).
I find that the slightly increased load of moving my eyes down to the lower left corner a worthy sacrifice for not being interrupted by a popup bubble. Interruptions also increase cognitive load, and should be reserved for things that are the most important.
One's interruption, is other person's expectation. If I have tooltips enabled, I am expecting them to pop-up. Whether they do that in the bottom left corner or next to my cursor is irrelevant in terms of cognitive overhead associated with a pop-up action itself, except that one that is not co-located bears additional workload akin to that of shifting your gaze away from the road to check on your cell phone who is calling...
Most of the time, most users will not need the popup describing the inlet, so most of the time it'll just be an interruption.
In my experience, I found that new users really need that guidance. If not, they can always turn the pop-up off.
Best wishes,
Ico