I tried emailing this but no reply, so will try this path..
I run a site called twitterfeed.com which lets users post RSS updates to twitter. As far as I can make out, pownce blocks requests to pownce RSS feeds coming from my domain (just a simple wget from the domain times out, while from other machines it always works).
I had a similar issue with del.icio.us, who have now helpfully whitelisted the twitterfeed.com domain/IP addresses - any chance someone at pownce could take a look at this, and hopefully do something similar?
Ariel recently mentioned that some of these "white pages of deaths" are caused by API users "abusing the system," whether intentional or not. She followed by explaining that they monitor for this and ban the IP if they see this happening.
So, Pownce team, have you guys thought about throttling instead of banning? You could do this automatically instead of having to manually watch for IPs to ban. It would certainly allow the developers of applications that use the API a chance to easily recognize the issue that their application is having an implement some sort of better efficiency (caching, or whatever they must do to cause lets hits against the database). At that, you could whitelist certain IP addresses to make sure that they are not throttled if you have previous arrangements with certain developers, or if you're not comfortable with completely relieving them of the throttle, you could place them in a special case class that could raise their throttle amount.
I realize that this is not the entire white page of death issue and that this may take some work to implement (or you may already have it implemented, I do not use the Pownce API), but if not it may serve as a way to help prevent these issues from occurring in the first place and allowing Pownce and its community a true chance to thrive.
(I'll stop being such a wind bag now that I've gotten that out of my head.)