Rated 3 out of 5 stars
It would be great if the placeholder was a small box with the alt text, or a clilckable icon.
The problem I need something like this to solve is when you are trying to read a blog or something in a reader, and you get huge (at least for a netbook, or anything less than a sideways HD screen) image which pushes any interesting text two pages down.
This removes the image content, replacing it with a huge box, still leaving the text buried somewhere I have to scroll to get to.
This only seems to happen if there are dimensions specified for the image, but they should be removed or otherwise disabled too.
(An enhancement might be to reduce the image to a thumbnail. say 16x16 or 32x32). It wouldn't save bandwidth but would save screen real-estate.