It certainly seems that way according to this article.
Google released a new mobile navigation app today and GPS navigation companies such as Garmin And TomTom saw their shares take a plunge. The announcement shaved $1.2 billion off of Garmin’s market cap alone. Its shares are down more than 16 percent so far today to $31.60. TomTom’s shares are down 21 percent to $8.11.
I haven't used the app but from what I can read from its features it is a serious contender to these two companies. The idea of using your cell to get driving directions and having the speaker phone tell you when to turn is a game changer. Add to this the fact that it is free and we might see the slow death of the GPS stand alone device.