After putting off visiting Iguazu Falls in Brazil because of visa issues I decided to use the visa I obtained to visit Bonito to finally visit the falls as a daytrip from Cuidad del Este.
The short version - I didn't need to wait. I took a taxi from my hotel and we crossed straight over the bridge into Brazil and to the falls, and returned just as easily. There weren't any checkpoints, gates or customs officials wanting to see anything.
The driver said it was a free entry zone. I had heard this before, but wasn't sure it was true.
I didn't continue onto the Argentinian side, so maybe someone else can help with that.
There is a customs office on the Brazilian side of the bridge if you want to legally enter Brazil and continue on, but it was way off to one side.
Additional info: The taxi cost 300,000GS including return trip, and the driver came with me as a guide through the park. I stayed at the Hotel Austria, and they arranged the taxi.