Rich Owings of GPS Tracklog offers advice on must-have and less-worthwhile features for an automotive GPS. I’ll slightly dissent from Rich on the value of traffic information, although of the units I’ve used the Dash Express has the only helpful implementation* of traffic I’ve found so far—and with Dash leaving the hardware business it’s not clear that anyone will be filling the gap in the future—although TomTom’s HD Traffic is allegedly headed stateside in 2009.

* Virtually all of the existing products focus on Interstates and other freeways, which might be helpful in really big cities where there are multiple freeway routes to the same destination, but isn’t so helpful in the places I’ve lived where the question is not “which freeway should I take?” but “should I take the freeway or one of the 2–3 surface street options?” Dash at least has some data on traffic on the surface street network—but much of it relies on Dash getting more market penetration, which seems unlikely unless they’ve hooked up with a major player like TomTom to provide traffic services going forward.