Sometimes it has network connectivity issues that prevents the app from working -- even if you download the "offline" app.
Like 2 days ago I couldn't add text to an image because the font list couldn't be loaded over the network due to the site having connectivity issues (and it doesn't work when offline). I had to resort to using gimp otherwise it would have delayed a video from being published.
Of all of the online or offline non-Flash image editors that try to replace Photoshop this one is my favorite. I hope it continues to get more developed. It lacks a lot of things but it's good enough for whipping together basic multi-layer layouts. Little things like being able to auto-center things vertically and horizontally by just dragging things around saves so much time. Also supporting Photoshop style layers for doing outlines and shadows speed things up.