OK, I'll take a shot at this...

PJ (or do you prefer Patrick?):

The only time I've encountered the non-wiping that you describe was when
I went skiing and the wiper blades were so cold/caked with ice that they
froze in the position they would be in if the blades were parked.

OK, that said, I would begin your troubleshooting by removing the blades
from the wiper arm and looking at the assembly; what happens when you press
on the center of the blade?  Does it spring back with some energy, like it's
supposed to?  I would suspect that you're getting some binding where the 
rubber blade slides by the little metal tabs that hold the rubber blade in
place.

Uh, Ric, yours is one that I haven't encountered, and we have the same
vehicle; be that as it may, here's my best guess(es)

1) Ya didn't clean the rubber wiper crap off your windshield like yer
supposed to!  ;)

2) You drive too much in windy conditions.

3) Your wiper motor's messed up; you need to buy a Ford Windstar ASAP!   :)

4) Your wiper relay rods are messed up; see #3 above...

5) Your blades are too long and hit the windshield frame; see #3 above

There, see how easy it was to fix your wipers?

Good luck, guys, I hope you rectal-fy your wiper maladies!

Norman
Leong@Baynetworks.com
'93 T4 MV