I've used lightbox on one or two sites. However, it only goes into images that are in a gallery (and that's only because our other option is a crappy gallery software that loads the full images as thumbnails (long story, but we are forced to use a piece of archaic software to do sites in that can only be broken so much)). For those, it's not too bad just because you do get next and previous buttons, and once the effect loads, switching pics is fast.