The DigiNotar root CA has been compromised and has been blacklisted by Mozilla and Chrome. I've already un-trusted their root CA in Keychain on my OS X devices, but how can I do something similar on my iPhone and iPad?
Edit: I'd like to do this without having to jailbreak any device.
Edit: The i0S 5 update from Apple removes the DigiNotar root CA from your iDevice and also gets rid of trust for MD5-signed certs. See this Ars Technica article for details.