I just jumped on the iPad navigation bandwagon, and I thought I would offer an update to using the "topo maps".
It is pretty nice. Topo maps/usgs aerial images/street maps are all included. It looks like they addressed the complains about not being able to see what you have already downloaded.
You can download 100000 tiles at once (which is about 1/4 of Washington state), and it takes about an hour for me (May depend on your internet speed of course).
It doesn't appear that you can get direction to a location, rather just see where you are, or finger drag to other locations.
Gives coords, elevation, heading, speed, and sunrise/sunset times (any two displayed at once).
I have all of Washington state/ the north half of Oregon, and the100000 tiles around Moab downloaded, and it together with all the basic small apps total 11 gbs.
For all my backcountry needs, this is exactly what I am looking for. This combined with a street gps (searchable address w. Directions) will take care of all my offline navigation needs.