Thank you for answering, Hilary. I figured this out, so I hope this helps someone else.
Found this interesting that I never bumped into this before, but you cannot set the value of a people picker out of the gate if it is inside a hidden section unless that section is within the same one that helps show that section.
Field in Section 1: dropdown choice with values "New", "Old"
Field in Section 2 (hidden until the ddl is changed to "New"): people picker.
Rule, when Section1: dropdown changes, show Section 2 with the people picker inside it
Rule On Load, or on Change for the dropdown: Set the current user using GetUserProfileByName.
This won't work on form load and won't work the first time you change the dropdown. Interestingly, it will work the second time you select a value.
In this instance, I want to show the Logged in user only after the dropdown unhides Section 2. So, I created a new nested hidden section inside Section 1 and called it HiddenUserSection. This is always hidden and I placed the people picker in here. This will update.
Now, I placed a Calculated value in Section 2. I point this to the people picker. Now, that value loads and cannot be altered.
I gave the calculated value borders to make it look like the other fields. :-)
Sean