When PowerPoint goes into full screen mode it will use the entire screen for the slide show which obscures the GP4 application.
There are, however, several workarounds available to hosts in order to have access to the GP4 interface to monitor the text chats, participant list and general controls.

The first option involves using two computers for the GatherPlace meeting and there are two methods hosts use to accomplish this.

If the host has two computers that are near each other, they can host their meeting from one of the computers (computer A) and then join the meeting from their second computer (computer B) which contains the PowerPoint presentation.

Then, using computer A, the host grants presentation rights to computer B which has the slide show running in full screen mode.

The host can then monitor the participant list and text chats on computer A and advance the slides on computer B as needed.

Once the slide show is finished, the host can revoke the presentation rights from computer B and resume sharing the screen from computer A if needed.

The second option for using multiple computers is similar to the option above but instead of the host using two computers, they have an associate help with the presentations.
This way the host can start the GatherPlace meeting and then pass presentation rights to their associate, who has the PowerPoint presentation running in full screen mode.

This option involves using the 'Window' mode when running the PowerPoint presentation and using Application sharing*, vs. Desktop sharing, in the GatherPlace meeting.
This allows the host to make the PowerPoint window as large as possible while still being able to see the GP4 interface to monitor the text chat, participant list and other controls.

This article shows how to use this option in a GatherPlace meeting.

*Note: Application sharing is currently available to Windows users only.