We've developed an 'orm documentor' app which reads the DevForce .orm file and generates all the overrides and puts them in a .cs file. It generates complete 'skeleton' classes which include the property and relation property definitions along with comment sections.
We then include the .cs file in our solution and edit it to add the comments to each property.
If we re-run our documentor we can point it to our existing .cs file so that it picks up any existing comments and includes them against the relevant property when the file is regenerated.
At the very least it would be great if the ORM allowed you to define a comment against a property. Would seem to be a fairly simple enhancment because it's just some text that gets saved away in the .orm xml file - no validation required!