NO! GPS IS FREE ALL THE TIME!
XM Traffic feature does require a subscription to work and to elaborate..
XM Nav Traffic is a seperate subscription..
You would have to pay for XM Radio and XM Nav Traffic seperately.. although I think they will cut you a deal if you buy them both instead of one or the other.
Edit: You get a free 3 months of XM Radio when you buy the Z.. and you get like 1 week of free Traffic (maybe less not sure).. XM Traffic is fairly cheap and I think it's pretty worth it honestly.. they seem to keep the updates going strong on real-time traffic jams.. Although i'm not sure if the GPS unit automatically provides a detour if it sees too much heavy traffic or not. This is something I would like to find out.