The question people should ask is whether any photo hosting site is good for long term photo storage. They are all under the same pressures to make money one way or another. They all can change their teams of service any time they want to.
I believe it is best to always have a backup.
Photos are an interesting thing for archiving or keeping long term. I have photos that are over 100 years old. Back then, people took very few photos. I have many photos that my dad took and are still in good shape.
The photos you took on your camera or digital phone yesterday...how will someone see them in 75 years. We have problems just keeping photos from a year ago. Will technology in even 20 years be able to read your current digital photos.
Even if the technology is available, how many pictures to be stored. Many people shoot zillions and post them on websites everywhere. Do you keep all your pictures, do you sort them, and how can you find them. How will you pass down pictures to your kids and Grandkids.
The entire digital picture storage and archive issues are huge.