We've seen a number of reports in the forums and on twitter about confusing results when you customize ClassificationFormats in Intellipad. Here are a few known pitfalls:

1. If you run with UAC turned on and your changes are not getting picked up at all, you might be running into a virtualization issue described in this blog post. The January CTP should help avoid this issue but if you're using another editor to edit your XCML file (why would you do that?), that app might not be "UAC aware" and it will run in virtualization mode leading to this issue.
2. If you choose to back up your original ClassificationFormats.xcml file, make sure change the file extension or back it up somewhere else. Intellipad loads all XCML files in the directory so changing the filename is not sufficient.

Thanks to all of you for your feedback and help in figuring out these issues!

-hoop