Johan,
Excellent work!
You can choose to just ignore the x,y values :P I agree that the dialog is not up to Inkscape's standard, and should be redone in 0.47.
I think the dialog *should* have the coordinates of the anchor point (makes precision placement possible, of course, which many people will want).
To make the dialog about 1000% more intuitive :) you could just change some text and rearrange stuff, at least for this release.
------------------------------------------ Guideline: (guide name) Current anchor: (x,y - a degrees)
Move anchor to: x position: [x] y position: [y] unit: [unit selector /]
Set angle to: angle: [a degrees]
Relative move [] ------------------------------------------
This (or something similar) would make everything a lot clearer, if there's time for it.
Again, excellent work!
JF