The “x-ray” interface that displays two layers of information in one view is generally a cute idea that doesn’t work well in practice. To see an example of this done very well, look at the London Multimap with the aerial photo overlay at Multimap.com. Amazing what you can accomplish with enough JavaScript. I hope this kind of view will become standard at the various mapping portals around the web. The next thing I’m waiting for is the ability to zoom in for a 3-d view of tricky intersections so I can rehearse what to look for in bizarro urban driving situations like you find in Europe (and Boston).
[Note: actual driving conversation from a summer trip to France]
NED: Are we on the road to Coulommiers?
JOE: It said “Chailly En Brie” on the sign. Is that the same direction?
NED: I don’t know. According to the map, we should be on the 402.
JOE: I haven’t seen any numbers on any of these signs. Wait! That said 209. Is that good?
NED: Let me see if I can find it. Is this Coulommiers?
JOE: Should I take this left turn or this hard left here?
NED: What? Oh, I can’t tell from this. Just keep following that truck.
JOE: We’re going in “direction Boissy-le-Chauffry” now. Is that good?
NED: I can’t find us anywhere on this map.
JOE: I think we should’ve taken that left back there.
NED: Are we on the road to Coulommiers?
Rambles Blog at Star Chamber 
Yes, this overlay is pretty useless, as slick as it is. I hate “brushing” for the data I need.
This mapping site does do some other things better than the ol’ standards. The images look much more like real paper maps, and they cull the data better based on zoom. I also like that they give a “permalink” at the bottom of every page. Look, here’s my house:
http://www.multimap.com/map/browse.cgi?lat=42.3419&lon=-71.0694&scale=5000&icon=x