I like using this for ajax file uploads. For example, in a photo gallery with thumbnails already occupying the client area then it's a convenient place to indicate upload progress from a drag + drop without placing a temp element in the grid or overlaying some other element with progress info. I'm not sure how well it solves the problem (usually I'm just interested in general file progress and not a specific percentage) but it does give a good indication of progress in a convenient location.