The major challenge in an AD RMS implementation is not getting the infrastructure up and running or getting the client settings, files and application deployed to all users. It's not making RMS available through your firewall or getting it working with your SharePoint server. No, the major challenge is getting your users to actually use RMS to protect e-mail messages and documents. It's very simple for your users to apply RMS protections to an e-mail or document--it's just a couple clicks--but it's hard to train them to remember to take that extra step. Luckily, there are solutions available to help you automate protections, so you're not entirely relying on your users to take that extra step.