Looks aside, there is a difference.
* Older chrome lenses and modern chrome Leicas are brass and heavy. However, chrome on brass is very durable and I like the weight and look if I don't have to carry too many.
* Black lenses, whether anodized or painted, will eventually chip (unless you are compulsively anal or don't actually use your equipment). That being said, chips don't hurt anything except pride of ownership. Plus, since they are almost always aluminum, they are alot lighter.
I have both and mix and match as required. Any combination looks cool in my eyes.
However I do agree that chrome may be making a comeback. As visiondr said "chrome is the new black". I especially like the silver paint aluminum mounts by CV and Zeiss as the sctatches don't show.
From a purely esthetic point of view, a nicely worn black painted, brass lens really rings my bell. Mild brassing on a matching lens and body makes me feel like putting on a beret and smoking a Gauloise while setting outside a French bistro.
Rex