I've just finished creating on-the-fly spatial indexing for shapefiles in SharpMap, and what an improvement !!! Rendering a shapefile layer to a map is now 5-6 times faster compared to a spatially indexed PostGIS layer. I'm now focusing on getting ready for the SharpMap v0.8 release, which includes the shapefile indexing, a new improved geometry object model, and a bunch of other changes and enhancements.