As if you need another reason to buy an i-Phone, there's a new app that downloads government raster charts, and ties them to the gps capability on the phone. Plot courses, create waypoints, zoom in and out. Wonderful! I just downloaded the program, so I have yet to become familiar with it, but so far it looks great!
MacENC looks pretty neat, but I think I'll stick with my free Seaclear on a PC for the time being. MacENC has some nicer features and support is no doubt better but Seaclear offers about 90% of the capablity for 100% less money.
I'm pretty sure the new iphone 3g has true GPS. I have one and it works quite well. It may use cell towers to get a general location so the GPS doesn't have to "work so hard", use extra battery power, etc. But it does have GPS. Here's a blog article that describes how it works. Link
BTW, I just bought the iNavX software last night ($49.95) and it looks great. I'll try it out on the water on Friday. I'll let you know how it goes.