Sorry. No answer for you, but I certainly sympathise. The inability to preview the focal point for radial Blur > Zoom is one of the great Photoshop mysteries IMO. Maybe the team thought that the introduction of Smart Objects in CS2 was the answer, but it still annoys me that I have to resort to trial and error. Something else that I can’t work out, is why the Alt (Opt) key while in the Zoom Blur panel, changes Cancel to reset, as with other panels, but clicking on Rest only takes the focus back the position it was in when the panel was opened. This seems pointless to me as you have no idea of the effect of any move without committing it — at which point that position becomes the new default.
Is there a way to preview the focus point? If not, can we add that to the wish list?
Yup, infuriating also to know that it is possible to insert a precise location for the lens flare filter by doing an ALT+click on the preview. Why not in Radial Blur?
With the radial blur filter you should be able to get back to the factory settings by holding down the Ctrl key while inside the radial blur filter.
The Cancel button should change to say Default when you press the Ctrl key.