CSV Grab - Date Format Question

I am using CSV Grab to import a number of fields and everything is coming in nicely with one minor exception.

In two custom fields I am using Date Field as the Field Type.

I tried entering it this way:

05/28/2010

and I tried it this way:

2010-05-28

but neither of them work correctly.

What is the appropriate format for importing date information?

Thank you.