It's got two major flaws, as I see it:
- It's a silo of data. Folks looking for images don't go to it first when they're looking for something.
- The UI on it for organizing images isn't nearly as nice as Flickr. I realize this as I use Flickr more and more for my personal stuff. Though MDID has a personal collection feature, there's no way I'd recommend it over Flickr.