1) I know Google Maps on the current iPhone supports Decimal Degree format for Long/Lat. I have tested this myself. I couldn't get the other formats to work though. The problem with this is, you can't get the maps without an internet connection.
1a) I'm doubting links on webpages with Long/Lat would work. Could be something Apple could implement pretty easily though.
2) a-GPS seems like it would be fine. It might take a minute to initially acquire a signal if you're far away from cell towers, but it's still your standard GPS otherwise. Seems like once you got a signal you'd be ok.
Think about the possibilities for exploring with GPS/topo/satellite imagery stored on the phone so you wouldn't need an internet connection. You would never get lost again...at least until your battery died.