Well, two sliders are sometimes not enough though.
Take the ExtractIsocurve command for instance. What I like about it is that you can hover over the surface with the cursor and get a dynamic preview of the isocurves at the current position.
It would be nice to have this kind of functionality in GH.
I'am aware that "nice" is sometimes not enough though.
:)
While I agree that 2D and 3D sliders in GH are a great idea...there are ways to do a 2D slider, even all sorts of custom interfaces through other hoops if needed (as we've already seen with the colour picker method): http://www.livearchitecture.net/archives/4489