I use GPSapp and it is useful to me in a limited way. It is complicated to set up, and tricky to use. But it is convenient to have routes on the empeg since I don't have another dedicated navigation system in my car at the moment.
Here is how it works. This is a simplified overview, without a lot of details. And it still sounds complicated. :-)
SETTING UP THE EMPEG SIDE OF THINGS:
You buy a GPS receiver/antenna with a serial cable connnection. Preferably one that runs on 12 volts so you don't need to build a voltage-reducer circuit for it. The receiver must speak NMEA (most do). Note: This can be just a plain old inexpensive receiver, not a full GPS system with a screen and everything. Most of these receivers are about the size and shape of a computer mouse, are designed to plug into the serial port of a laptop computer.
You install that GPS antenna in your car and wire it up to the empeg sled's serial port, probably needing to construct a custom cable for the purpose and needing some trial-and-error to get the RX/TX lines working right.
You install Hijack on your empeg.
You download the precompiled version of GPSapp from the web site and extract the archive. It contains many files but the file named "gpsapp" all by itself is the precompiled binary you really need.
You copy that binary to the player.
You edit the player's config.ini to launch GPSapp (using @DC).
You edit the player's config.ini to add a bit of reservecache (using @DC) so that GPSapp has got room to breathe.
You create a folder on the player to store programmed routes.
You edit the player's config.ini to point GPSapp to that "routes" folder you just created.
You go into the Hijack menu so that the serial port behavior is "Apps use serial port".
Okay, now the empeg is set up to use GPSapp...
SETTING UP THE PC SIDE OF THINGS:
You install a Python script interpreter onto your PC.
You extract the python script files from the GPSapp archive file that you got from the GPSapp web site.
You navigate to
www.mapsonus.com and create a user-account.
In your user account you have to set a few preferences, I think one of them has something to do with showing detailed route data or some such. This is what gives you the option of getting GPS coordinates from the web site.
You must remember that you have to sign in with this user account each time you want to put a new route into GPSapp.
CREATING A ROUTE FOR GPSAPP TO USER:
Sign in to Mapsonus and get directions so that it shows a route on the screen.
At the bottom of that route screen will be a link to "Raw Route Data" or some such. Right-click on that link and hit "save link as" (or whatever your web browser's option for that is), and save it as a plain HTML file on your hard disk.
Use the python scripts to post-process that HTML file. Instructions for doing this are at the GSPapp web site. The resulting file will be an ascii text file with a bunch of numbers inside it. Give this file a useful name such as "From home to Powell's Books". No file extension on the end.
Copy that file to the empeg and put it in the routes folder you created.
USING GPSAPP WITH THE ROUTE:
Get in your car, run GPSapp from the Hijack menu screen.
If it says "waiting for data from GPS receiver" for more than a moment, then things are wired up wrong. Otherwise, it should drop you into GPSapp.
Press and hold the bottom button until you reach a screen showing the satellites. You should be getting strong signal bars from three or more satellites.
Press and hold the bottom button until you see the map screen with the speed on the right side (hopefully a big zero).
Press the bottom button to open the menu and select "load route" and load up your route file.
A squiggly line should appear on the screen. Put the pedal to the metal and follow it.
ALTERNATIVE:
Buy a real GPS unit with a built-in screen, snazzy user interface, voice commands, high rez LCD color touch screen, built-in route finding, street maps on the screen, etc., and follow its directions. Much better. But also much more expensive.