I will also chime in on MacENC/GPSnav. I have used it for trip planning (I rent/charter boats, I don't own one right now) and seen it in play onboard, both as the main navigation system or to export to another plotter as noted N. Ivy. Really good and stable product. The fact that it readily imports and updates the free NOAA charts (and they have a low cost DVD with all charts to get you going) is a big plus.
I was VERY impressed by all the support I got when I was using the free demo version, and mostly complaining to them about all the things I didn't like about the Mac itself when we converted from Windows. Even though it had nothing to do with their product, they gave me a lot of helpful advice. I got the same on-the-spot response time noted above.
George