Add a file that has no image defined for the tag (I added an eclipse team project set, but I think anything that isn't an image that is dropped into the drop box will suffice) and the click on the dataset in the MyDatasets view, warning message pops up twice each time that object is selected.

2010-11-04 14:53:14.821 [pool-2-thread-4] WARNING edu.illinois.ncsa.mmdb.desktop.ui.pages.DatasetBeanPage.updateData(DatasetBeanPage.java:163) - No image available for: tag:cet.ncsa.uiuc.edu,2008:/bean/Dataset/038925f8-9a39-4d9f-89eb-0624b6dc6ad2