One argument for splitting the existing Geoprocessing forum (or at least reorganizing it) is that it currently represents nearly 50% of all the forum threads/posts on the Functions topic. If you were a lumper, it could be argued that many of the other functions such as Geocoding, Map Automation, Interoperability, Imagery/Raster data, etc. should also be included as aspects of Geoprocessing. Doing so, however, would raise the "market share" of the Geoprocessing posts to roughly 65-70% of all the forum posts! Personally, I am a splitter rather than a lumper.
My suggestion is to keep the Geoprocessing forum as is and create a new forum simply called "Scripting". Keeping with the spirit of v10 (arcpy scripting being a major aspect), this potential Scripting forum would be the go-to place for posts regarding geoprocessing, mapping, spatial analyst, and geostatistical scripting.
Scripting (that is automating GIS "work" using a relatively high level computer language such as AML, Avenue, Python, etc.) is a central component of any reputable GIS. I for one am extremely excited that ESRI is putting a renewed emphasis on scripting in v10 (arcpy.mapping). Doing so is truly helping to rekindle the GIS Analyst caste that was, I think, somewhat lost when ESRI abandoned their old scripting languages like AML and Avenue and jumped head first into using ArcObjects and "real" programming languages as their default GIS automation technique.
Scripting deserves it's own forum.