Does anyone here do it and is the benefit enough to justify the expense of the ethernet box and cables? I'm thinking it would be nice to be able to "see" either transducer from either end of the boat.

Yes I do. I have Low hds units and they are connected via Ethernet and NMEA 2000 network. I do it mainly so the wpts are synced no matter which unit I use to mark them.

I network units when I install them. Depending on the units, there is different advantages of networking.
John

It all depends on your style of fishing.

I crappie fish (tournaments) and do not link my units. I simply find my structure/fish and mark a way point. I then head back to my way point and when the structure/fish appear on my display I toss out a buoy marker. I then get on the trolling motor/bow unit and head for my buoy marker. When I see the structure/fish appear on the bow unit I simply mark another way point. Now I have my way points saved on both units and I am more accurate on my GPS and use my buoy marker as a reference.

This may be a Humminbird specific question.. Is there any information that the networked units do not share besides chart info off of the Navionics or Lakemaster chips.

An Ethernet connection between Ethernet capable units will share Ethernet accessories (RADAR, 360, etc), GPS data, GPS antenna, Temp sensors, and transducers.

Sonar technologies can be shared if you have current units (XX9 series).
A DI or 2D unit will display Side Imaging from a Side Imaging unit via Ethernet. A 2D or SI unit will display Down Imaging from a Down Imaging unit. All three unit types will display 2D from another unit using the same 2D frequencies.
All three unit types will support the 360.

Mapping is NOT shared.

What do you want shared that is not listed above?

I think that covers it. I was just wondering. I have an 1199 and a 999. I would like for the person in the front and back seat to be able to see data from either or the same transducer, whatever is desired.My understanding is I would be able to run the trolling motor with the MinnKota remote(I-Pilot Link) and also either FF screen, with the understanding that doing if from the display is probably a PITA.

It takes Lakemaster map software to use the mapping follow-the-contour feature.

Otherwise the iPilot does its own thing independent of a sonar/GPS unit

I understand but if the units are networked, the Ipilot will follow the contour of the Lakemaster regardless of which unit it's in, correct?

Correct, assuming you have a Lakemaster card in both units, or remove card from one unit and put it in the other. Your active tracks spot locks will also appear on both units as well. I have 2 1199s networked with I pilot link and like it a lot. I really like the link system cause it allows you to navigate between waypoints and spot locks with ease of a remote. Just pull em up on remote and go to it.