We just returned from POR yesterday! It was pretty busy since we are in Spring Break season. However, we only waited for more than 10 minutes on a bus ONE time and that was at Boardwalk, not POR or a park! We had taken the boat from Epcot to BW so we could get to DTD for our dinner ADR. We waited about 15-20 minutes there.
At POR, we never waited more than 5 minutes for a bus. We always used the main depot though. At busy times in the mornings, our bus would be full by the time it got to the East Depot and we didn't stop so my guess is that those people might have waited longer for a bus. We had the same luck in the parks with buses. I think we waited almost 10 minutes at Magic Kingdom for a bus back to POR, but almost every other time, a POR bus was pulling up to the stop as we got there! We talked all week about our "good bus luck!"