The second you snap a photo or press the stop button when capturing a video, they start uploading to your Dropbox account, similar to what Windows Phone does with SkyDrive. You can, of course, permit this function only over Wi-Fi or forbid it altogether, but it does take the hassle out of keeping backups of your gallery, since it doesn't have file size limits, so that huge video is welcome too.
After the first 500MB of uploads you get another batch, and so on and so forth, all the way to 3GB. Not an insane amount of storage, but it's free and will probably suffice to sync a holiday's worth of photos and videos while you mooch on the Wi-Fi in the hotel lobby. The downside is that the new update requests way too much permissions, including account ones, so people have been venting their frustration over this in the comments.
source: Dropbox (AndroidMarket)