Image via CrunchBase
And since that was a really long sentence, let me explain. I don't upload enough photos to Flickr to justify a Pro account, so I've never upgraded. Instead, I just put the thumbnails on a webpage or in a blog post and link them to the photo page. Flickr makes it easy by providing the code. Then, should I ever want to use those photos for anything, I can still find them.
Yesterday Cory asked me to remove a picture in one of my blog posts. I thought I could just mark that photo as private, and I could still see it because it's my picture, but no one else could see it. Wrong. As soon as I marked it private, I was redirected to a page that said I didn't have permission to view that photo. I hit the back button on my browser and tried to change it back, but that didn't work. As far as I can tell, that photo is gone, forever.
Yes, I have it here on a DVD, but I can't find it on Flickr any more.
Another tip for people like me who haven't upgraded to the Pro account on Flickr: tag all of your photos with your username or something unique to you. Then, you can always search Flickr for photos with that tag, and your photos will be the ones that come up - all there, whether they're still part of your photostream or not. Unless, of course, they've been made private. :P