If you've got existing Oracle Reports in an RDF file, you can create in Portal something called an RDF Access object. Basically wraps around the RDF to give you an easy way of executing the Report from Portal.
When you delete an RDF Access though, you'd expect that any object calling that RDF Access would also get deleted. That apparently is not the case--we just ran into a situation where there was a stored proc (created by Portal) that got left behind when the RDF Access was removed.
Normally not a big deal, since you'd never call the dangling proc. However when we had to apply a patch, of course the first thing it did was try to compile everything in the schema. Meaning that proc failed and thus blocked the patch from completing.
How very very annoying. Luckily I was able to use the Portal UI to search for the proc and edit out the reference to the now-deleted RDF Access package.