The culprit here may be that our plugin currently overrides WordPress comment pagination. This effectively means WordPress will render all ~1,800 comments server-side (i.e., in the page's HTML) even if you have pagination of comments enabled in WordPress itself.
While this on its own is not troublesome, it can slow down page load times (as you're currently seeing) on sites that use lots of plugins, large plugins, poorly-coded plugins, a large theme, strict server settings that can't properly handle rendering this many comments, etc. There are a lot of factors that are in play here.
We're looking into addressing this in a future release of the plugin. In the meantime, two things:
1. The affected page to which you linked does still load intermittently when we look. Here's a screenshot of what I saw after refreshing the page: http://dl.dropbox.com/u/15229959/Screenshots/0vg.png
2. Temporarily reverting your site's theme to the default WordPress theme and disabling all plugins except Disqus -- this is only for testing purposes -- would help determine if your theme and/or plugins may be affecting this situation. If you decide to give this a shot, we'd really appreciate it if you could let us know what you find at http://disqus.com/support (be sure to include the debug info found under Advanced Options in the Disqus plugin as well).