We're using OpenX to serve ads on a number of sites. If the OpenX server has problems, however, it blocks page loads on these sites. I'd rather have the sites fail gracefully, i.e. load the pages without the ads and fill them in when they become available.

We're using OpenX's [single page call](http://www.openx.org/docs/2.8/userguide/single+page+call), and we're giving divs explicit size in CSS so they can be laid out without their contents, but still loading the script blocks page load. Are there other best practices for speeding up pages with OpenX?