Disqus is in the Content category, which isn't blocked by default (reason: users seem unhappy when we block content-y things like videos, photos, and comments by default). But you can still check the adjacent box to block Disqus (your settings are remembered on a per-site basis).
OpenX, otoh, should be in the Advertising category and be blocked by default as far as I know. Is there a site where this isn't the case?
Ok, thanks. I prefer to block everything by default, so for me per-site basis is not very convenient. In the case of Disqus: on most websites I don't read the comments and I prefer to block all the requests (mostly 100+ if you include the gravatars).
With Ghostery I just block everything, but this is also not perfect because, as you mentioned, you sometimes don't see all the content. It would be nice if the add blockers could block content in the way Chrome blocks plugins: everything is disabled, by you have a placeholder which informs you that something was blocked, and when you click on it, it loads the content.
OpenX is indeed blocked (I checked it with the chrome dev tools), but it doesn't show up in the Advertising category, e.g. http://www.openx.com/.
OpenX, otoh, should be in the Advertising category and be blocked by default as far as I know. Is there a site where this isn't the case?