I've been helping out a little with the linux-based GPSdrive program. While true that we're only using static maps right now (which are a PITA for things like route planning!), we are also moving towards using vector maps. It's slow, because there are no full-time developers on the project, but proper maps are coming.
I haven't played with a mac for about 4 years, and I've only worked with OSX a few times. Now, though, I'm looking at the minimac and salivating... I've discovered that there are Mac ports of Gtk (which is what GPSdrive uses for UI display and drawing). I suppose we'll have to eventually code a proper Cocoa interface, but I'll be trying out the Gtk port.
Anyway, it's an option.