I think it's safe to presume that Navionics Mobile Marine is the best selling iPhone charting app in the U.S. and many other countries.  In fact, as I just wrote in an April Yachting article, many iPhone boaters consider it a "no brainer" even if they also use other nav apps. But lookee here, they've rebuilt the entire thing, substantially improving both features and value. Today you can buy the US East Marine and East Lakes versions for $10 each, a steal really, but they are 166 and 535 megabyte files, which is a bit of an inefficient pain for all concerned.  By contrast, the new $10 Marine&Lakes:US will be an easily updated 2 MB because it doesn't come with data.  BUT you'll be able to download charts and lake maps for anywhere in the entire U.S., quite easily, and fresh direct from Navionics' own servers. The greedy download illustrated above -- note the chart and POI detail of Newport -- took about 10 minutes via my home WiFi network, and a much smaller download went fine even over AT&T's poky Edge service.  And there's more...

The new Navionics Marine is integrated with the Google Maps app built into iPhones, which means that, if desired, you can have the water detail overlaid on satellite photo maps, street maps, or a hybrid of the two.  And you will so desire.  I have a late stage Beta version here, but it still seems faster than the original even with maximum land data enabled. Click on the collage below and start with the upper two screens. First you'll see the phenomenal amount of integrated land, sea, and lake data I now have in my pocket.  You'll also see that I've been giving the app a workout (without even a beta burp).  I tracked myself driving down to the Public Landing where I took a few photos, then finger tapped a route to Pulpit Harbor (though routes are mainly just useful for distance and fuel estimates), and then emailed both it and the track, photo thumbnails included, to myself.  (You can download the Google Earth .kmz files here and here.)  I also reported a couple of little chart discrepencies to Navionics (will the corrections show up on the phone eventually?), and then used the POI search feature to poke around Monterey, CA, where -- what the heck -- I downloaded some more charts.
    Navionics Marine will only include lakes in the U.S. and Canada ($15 gets everything for both those countries, by the way) but foreign regions will also be greatly expanded without added cost. For instance, Marine:Carib & S. America will be $20, Europe 15€, UK & Holland 25€, Denmark & Greenland 40€ (higher hydrographic fees, I think), and Australasia & Africa 20€.  I'm not sure how much coverage detail there is in those regions, but what is now almost 30 Navionics Mobile Marine regions will become just those seven.  And get this: Largely in the deference to the current owners of those 30 regions, which will be updated one more time and then discontinued, there will be a few-week-long introductory sale of the new apps.  Like $3 for U.S., $5 for Canada added, 5€ for Europe, etc.  Can you say "no brainer"?