We cooled off our feedburned fingers and extinguished the fox on fire. Everything seems working well now, at least from this perspective. Please share any issues.
The probable cause was the combination of an ASP.NET application setting and the GoDaddy banner script. We turned off this HTTP compression setting and from here everything is all good now.
What's more, the latest build of the used content engine looks very promising. As soon as version 1.2 is released, we will move the site into our existing, ad-free deluxe hosting plan. This will take roughly 3-4 weeks, but should not be noticable besides ad-free content.