For some reason, images from Imgur as well as in third-party advertisements (not directly related to Stack Exchange) are not loading. I only get alternate text in its place. I have no problems with any other sites and images that are part of the Stack Exchange interface as well as ads related to SE are loading normally. Bypassing and clearing the cache in the browser does not help, and it is noticeable on all SE sites Is there a problem?
I can see images from imgur just fine: http://meta.superuser.com/ads/display/2164
It could be a temporary issue from your location.
It happens to me as well when I'm at a client's premises. I don't care too much about the ads but not being able to upload to imgur is quite a pain in the neck. This LAN is actually severely crippled.
Another possibility is that you might be running add block plus. But this is easy to diagnose since you can temporarily disable this FF/Chrome extension or may be use IE.