OK, I've finally nailed down one of the specific reasons the new Convert Entities within the Intersection Curve interface is a problem.  I'm working on a project in v2009 now, so maybe this is solved in v2010--I'm not sure.

When I select stuff to convert to sketch segments with Intersection Curve, the green check mark does not dismiss the operation.  Fine.  So I click on the red X.  But then if I click the red X again, that cancels my entire sketch!  Not cool.  The green check should dismiss the feature/function, since as it is now, it does nothing.  The red X generally signifies cancel (in other features/tools) instead of "OK", so it shouldn't ever be used as "OK" to check out of a function/feature.

Why is this a problem?

I'll often (finally) hit the Escape key or the red X to dismiss the feature, then click again to exit the sketch.  But we've crossed functionality by making the green check null and void, so when I click and click again, this must be over the red X and then the red X again--once to escape the Intersection Curve, and the other to exit the sketch.  But instead of making a mere exit from the sketch, the sketch is erased!  I know lots of things were done to the interface to make it more consistent with other tools, but crossing the functions of the green check with the red X ("OK" vs. "Cancel-and-trash") is quite dangerous.  Perhaps it's time to look at this again and make the general purpose of each interface symbol consistent?