Finally, somewhere I think I can contribute!
This may seem crazy, but I'm going to disagree with the common refrain here about the inline images being sized appropriately. I find that they are both:
(1) Too small to be properly appreciated (I think this is where many people are coming from with the "click to zoom in or make it bigger" message), and
(2) Too large to mesh well with the text. I find the disparity in column widths to be quite jarring and think it really makes the feature articles here look less professional than they could.
I would like to propose two different classes of image: full-width feature images which "sell" the story--particularly the lead image showing a launch, satellite, or other concept, but other key photos throughout the article could be featured as well--and much smaller inline images which help the content flow by illustrating concepts and breaking up the wall of text. It would be great if all of these images could be clicked to cause them to expand into a floating shadowbox.
I agree with many others that captions would be extremely helpful, especially for the full-width feature images. I think NaN really hit the nail on the head in stating the usefulness of such captions. They are nice with inline images as well, but less important there as the image's purpose is less to illustrate a specific concept than to add some color and excitement to the article--perhaps these captions should only be shown where these images are expanded?
I also think some minor treatments to the margins around the images and a general adjustment to line-height are helpful in improving readability.
To illustrate these concepts, I have attached a few mock-ups prepared by lightly editing a recent article's CSS and content using Firefox's developer console. I hope these help illustrate these concepts and at least one possible implementation of the captions people are proposing.
(edited to remove accidental multiple copies of attachments)