<<Disclaimer: Verify this information before applying it to your situation.>>

Thanks for your responses.  Many replies noted the terms either THICKENING or
BAKING as to whether the starches are interchangeable.  My general feeling is
that you can use either corn- or potato starch if THICKENING a pudding or
gravy.  The cornstarch is clearer & gels more.   The responses were pretty
well split when it came to substituting cornstarch for BAKING.  I'd say it
leaned closer to YES you can substitute cornstarch when BAKING.

The consensus for using cornstarch instead of potato starch is:
YES   6
NO   4
NOT SURE   2

A couple points to consider:
...we typically substitute equal amounts arrowroot or sorghum when needed in
our recipes for potato starch.... Jay

...Cornstarch (as in pudding) thickens quickly, but will un-thicken (break
down) w/ continued cooking.  If you stir it after it is cool, it will not
form a solid mass again (think lemon merigue pie).  Potato starch takes
longer to thicken & can be cooked for long periods of time still stay thick.
It also forms a slippery goo--very elastic.  Sweet rice flour might even be a
better sub than cornstarch.

...Potato starch is a very fine flour, while cornstarch holds things together
like glue...

Thanks.
Wendy, Exton, PA