You can load it into an Unmanaged Raster Catalog which would leave the original image intact, and only create a pointer to it. Otherwise the performance is theoretically faster as the Managed geodatabase format tiles out the whole Ortho into much smaller tiles (default 256x256 in ArcGIS 10, 128x128 in earlier versions). So the processing it is doing is this tiling, which can take forever. Depending on the original format (not sure about ECW) the performance gain is huge because the entire image isn't needed to be read. It also recompresses the tiles from ECW format into its own internal format, which is based on GeoTIFF i believe.