Dropbox is a simple cloud app that can pretend to be storage space on your computer -- or on multiple computers. They'll let you use 2 GB for free, or a little more if you tout for them. After that they'll upgrade you to 1 TB, but you have to pay.
So far, this looks like a straightforward deal; just keep your usage under 2 GB, which is a lot of pictures even with the monster-sized files modern cameras create. But our family has been using Dropbox to swap pictures of a recent trip, and we've discovered some things about Dropbox that I want to pass along.
EDIT RIGHTS If you grant someone edit rights on a folder you share with them, they can put pictures in the folder. They can also delete pictures from the folder, even if you put them there. When you share it with three or four people, all with edit, things start to get crazy. Say Person B copies off the pictures he wants, and notices that his Dropbox is full; so he deletes them. Person C goes to get them, but they aren't there.
Regardless of the number of computers involved, there is only one shared folder. If you store something only in a shared Dropbox folder, you're hanging out there.
How easy is it to goof this up? If in Finder (Windows, read "Windows Explorer") I drag a picture from the Dropbox folder to a real folder on my computer, it's no longer in Dropbox. So I make a duplicate of each picture and drag the duplicate.
HIERARCHICAL FOLDERS Just as with real folders, Dropbox folders can contain other Dropbox folders. The "child" folders inherit the properties of their "parent" folder.
So, if you share pictures very often with the same person, you can save time by creating a parent folder for that person and granting him/her privileges on it. After that, you can make a new child folder in the parent each time you want to share pics of something that you want to keep distinct. You won't have to grant the other person privileges all over again; and the other person won't have to manually sync the new child.
SPACE MANAGEMENT How can two people, each with a 2 GB storage quota, run out of space when they've only stored 3 GB? Like this:
Person A had 500 MB in an unshared Dropbox folder as offsite backup. Then A and B go have fun together and A takes 1 GB of pictures. A puts them in a new folder, bringing his total to 1.5 GB, and shares it with B.
But B had an unshared Dropbox folder too, totalling 1.5 GB. As soon as B syncs the shared folder, B runs out of space. Dropbox offers to sell him more space.
Sharing works out swell for Dropbox, because the more people share a folder, the more times Dropbox can resell the same storage space. Their reasoning; if shared folders weren't counted against your storage quota, you could get unlimited free storage space for yourself by sharing folders with your friends. Now that's dishonest; who would ever do that?
To help you run out of storage space sooner, Dropbox doesn't provide any file compression option. (Flickr, on the other hand, does.) You can compress them yourself, of course; but you have to do it.