When working with an ArcMap layer which has many symbols based on bitmap files these performance problems may occur:
1) If applying symbology for a layer that uses bitmap picture fill symbols, ArcMap will process for upwards of 5 to 10 minutes.
2) If opening the Symbology tab in the Layer Properties dialog box for an existing layer that uses bitmap picture fill symbols, ArcMap will open the dialog box only after several minutes have transpired.
Internally, ArcMap is inefficiently managing each bitmap picture fill symbol. As a layer references more of these symbols, ArcMap operates slower.
This issue is resolved in ArcGIS Service Pack 1.
<a href='http://support.esri.com/en/knowledgebase/techarticles/detail/24854' target='_blank'>[O] ArcGIS 8.1 Service Pack 1</a>