Driving around the South Bay, I tested 101, 85, 280, Lawrence Expressway, and Montague Expressway. The experience was flawless, with two surprising exceptions. First, it dropped out briefly around 85 at El Camino, center of the commute path for folks heading to Google, MSFT, and the other companies in Mountain View.
The second, however, was even more odd. Heading down 280 south at DeAnza, the radio dropped from 3G to Edge to nothing. Those in the know will recognize the location as being right outside Apple HQ in Cupertino! A friend suggested that the failure was due to heavy usage within Apple. That may be the case, but it is pretty odd. Area in La Jolla near Qualcomm HQ must have at least as much usage, but I haven't experienced failure around there yet.
It appears that Apple and AT&T need a little more cooperation.
Even with the dropouts, though, I must say that they were brief and definitely provided an experience as least as good as satellite radio.