Do GPS navigation systems encourage unhealthy behavior?

A few weeks ago I bought a Garmin nuvi 200, a low-end (euphemistically referred to as "entry level") GPS navigation system for my car. Despite costing only about $200 the device works great and I've really enjoyed using it. I don't see any good reason for the typical driver to get a more expensive version.Like any decent navigation system these days, it provides an estimated time of arrival. The estimate changes as you drive, and of course with traffic the initial estimate is often optimistic. But after using the thing for a while I realized that the estimated time of arrival recedes when I'm driving the speed limit. As best as I can tell, the unit bases its arrival time calculation on the speed limit plus 10%. In other words it assumes you are speeding.I can't imagine I'm the only one who dislikes seeing their estimated time of arrival getting later and later and I bet some people decide to speed up as a result. I decided to ask the company about this, using the feedback form on their site.Here's the reply I received:

Dear David Williams,Thank you for contacting Garmin International. There is a proprietary algorithm used to determine all of that information. I know distance and speed limit, along with speed of travel all go into this calculation.With Best Regards,Matt KelleyProduct Support SpecialistMarine TeamGarmin International

So there you go.Anyone else have a similar experience?