Please use multiple out-of-process threads for GP Tools when possible. Some of this has already started because now at ArcGIS 10 the Geoprocessor has become out-of-process; where the real work is now done in the ArcSOCP.exe and ArcSOMP.exe vs. the ArcMap.exe and the ArcCatalog.exe. I realize that not all GP tools can easily be multi threaded but some can. As an example the ‘Add Rasters to Mosaic Dataset’ GP tool could be several simultaneous processes because several processes can write to the Mosaic Dataset tables at the same time. (If is an SDE MD). I have several servers and workstations that have 8, 16, and 32 CPUs...and sometimes more. It would be nice to take advantage of this when possible.