I have 2 J2.5 sites and 1 J1.5 site using this plugin and on 2 of the three all is good! One of the J2.5 sites doesn't seem to do anything with regard to Disqus in any of my content. I installed the component and the install went flawlessly. Both plugins are there, enabled and configured with the correct shortname. I have triple-checked the settings and since it is configured for all menus and all categories are selected.
I know there isn't an issue with the Disqus account as all three sites use the same settings/shortname. Also, I am using the Disqus plugins for both Sobipro and EasyBlog and they work fine with that same shortname.
Are there are any "common" issues with this that perhaps I'm overlooking? how about any uncommon issues? It doesn't seem that there is much to do here. It's been a while since I installed it on my other sites, but I seem to recall it just worked!
UPDATE: I tried hardcoding the Disqus code into an article directly as obtained from the Disqus site for my URL and it loads fine so I don't think this is a script conflict. It appears that the plugin simply isn't working for some reason.