The Droid GPS uses Google Maps to provide turn-by-turn directions or a list of directions. You can add layers to the map for satellite view, traffic, gas stations (with gas bot) and Latitude. You can change the route based on a list of alternatives that it provides, but I don't think it provides a complete trip planner for different stages.
Would be nice if it showed the posted speed limit and your current speed like a Garmin does. Time estimates, near as I can tell, are based on posted speed limits, not current speed.
In my opinion, it is a good alternative to a Garmin or TomTom. If you are going to buy a new phone and a GPS, then save yourself some money and buy the Droid.
Coupled with Google's voice search, this thing rocks. Just say the name of the store you are looking for and a navigation link appears in the browser letting you get turn-by-turn directions to the store; no searching for addresses or typing required.