It appears that there is currently no support for transparent gif or png user maps. This would really be nice, if for no other reason than just to not be constrained to only rectangular map overlays. (Better overlaying of contours would be nice too though.) Although the alpha blending gives decent visibility through the 'transparent' areas that get shown as white, it doesn't look nearly so nice (like looking through a fog). If I remember correctly, the waypoint symbols are actually transparent bmp. So I would think providing similar capability with user maps should be fairly straightforward.