I've been trying to get this working for months, but the break through was the fact that yesterday I found that OpenVPN have released about 2 weeks ago their own free iOS VPN application,
OpenVPN Connect, that ties into the VPN API within iOS 5.0 and above.
After some research, I was able to get it working using a single file (importing the text from the other files within the client bundle into the .ovpn file). While this isn't the most secure method (if anyone else got hold of it, they could connect to my VPN, and the certificates aren't held within iOS secure keychain), it is the easiest for deployment. Once the iOS app is installed, the user just needs to open the email with the .ovpn file attached, click on it and import it into the OpenVPN application.
There are a few things to note,
dev tap and
tls-remote functions don't work with the iOS app for various reasons, so you will need to comment them out of the .opvn text file. Also you have to use TUN style tunneling instead of TAP due to the iOS VPN API.
Hopefully this is enough information to help people to work out how to set it up, but
I've also added a lot more details on a blog article I've published here.