I love the convenience of having my photos online and share-able, and especially having them backed up automatically as I take them, but the problem is that all the major sites seem to have a dream of being the last internet site standing, and want to keep all your photos in their little universe. Shutterfly, Facebook, Google, Flickr -- they tend to only allow sharing within their little universe (though I am hoping for good things from Google peeling photos out of Google Plus).
Basically, sending your photos to these sites is a bit like sending someone to North Korea - they go in but never come out. Someone just shared a shutterfly album with me and God forbid you want to actually save some of the full-resolution images rather than just buy prints from them. At best these sites have some kludgy way to download full resolution photos one at a time, but it is never, ever easy and none have, as far as I have been able to see, a batch download function. Flickr is the best in several ways due to its API that lets me automatically share albums and photos pretty easily in WordPress, but its core interface is now so ugly with the revamp a few years ago that I can barely stand to open it (and they tend to change names for the same damn thing - set, album, collection, etc - depending on which menu or context you find it).