OK, solved the issue myself: The plugin on the marketplace is NOT up-to-date (if any RapidMiner folks are on this forum, pay attention...
So to get the IE plugin to work correctly, you need to download the latest jar here:http://sourceforge.net/projects/ieplugin4rm/
Uninstall the Marketplace version, if you have it installed.
Then, place the jar (rapidminer-Information-Extraction-1.0.2.jar) in your $RAPIDMINER_HOMER/lib/plugins directory.
To get the examples I mentioned above, do:
svn checkout https://svn.code.sf.net/p/ieplugin4rm/code/informationextractionplugin_Vega/trunk/informationExtraction_Vega/samples/
mv samples ~/.RapidMiner/repositories/MyRepo/
Finally, the IE plugin works! (Well, the examples, at least - still have to see if this is generally true...)