I went to Yellowstone with a friend on July 4th vacation. We drove there overnight from Park City, Utah and got there around 6am to grab a campsite - there was a line! Luckily we got a campsite for 3 nights. We both were pretty active and loved hiking so we went hiking everyday (6-8 miles.)
I knew Yellowstone was quite popular but didn't realize it would be SO CROWDED! Tourists are more than wildlife - and they would stop for wildlife.