The newer digital cameras are getting much better with respect to lightning. Some of the shots I've seen are great, but when I look close here are the areas I'd like to see digitals handle lightning better before I buy one:
1.) Distortions/ghosting from closer or more intense bolts. While I have seen some exceptions to this, most very bright or close lightning strikes have big problems exposing correctly on a digital camera. This type of shot is hard to get and usually ends up being a prized catch on slide film, one you'd hate to lose due to distortion problems. Halos, 'smearing', ghosting, saturation (white-out) and overexposure of the main channel (unusually fat, wide bolts rather than crisp, narrow detailed ones) seem to be the main problems here.
2.) Cloud base ambient light reflection color. The orange/brown hue to the clouds from city lights, especially lower clouds, is a detractor on digital shots. I don't run into this quite as much with slide film.
3.) Noise from long exposures, though as mentioned before this is getting better.
Digitals, in my opinion, have a long way to go before they can compete with the old manual SLR and slide film for lightning shots. For just about everything else though, the digitals have got it made.