I have iPhone 4 with max memory and iOS v4.2.1.

I do get memory warnings on launch when I have lots of apps running (Full iPhone's Memory.. Too many apps are running in background. Please turn off and restart your iPhone, or close some of the background apps). Sometimes I do have to go into the multitasking area and close out some of the other apps. I just checked my Navionics East Coast and it seems to be working fine. I use BC Canada (which includes Seattle) all the time and was on the US West app a couple days ago, no problems.