Good analogy, Mark... but I think it's more like a Ferarri and a Pinto with multi-color paint and stupid stickers all over it. LOL
I've used Flickr since almost it's inception, but man has that place lost it's appeal. It's like a flea market now, filled with junk and horrible flashing, blinking, stupid banners everywhere.
I'm really glad 500px has come along and that it's gaining in popularity - as I'd stopped using Flickr because all of the stupid badges and spam-like comments.