I'll just throw in my .02 here.
I prefer dedicated units, I like the idea of 'all in one' deals, but if it craps out, it ALL craps out. For me fuel status is a high priority. I trailer and fish not only off the NC coast, but up in Mass, Fla in both the panhandle and in SW Fla as well and I got a "feel" for the range of the boat depending on conditions and how I run it,,, but it's always good to know what "is" in the tank and what you got left, what your burning and etc.... especially if fishing offshore dependant on weather conditions and sea state.
I do not have first hand knowledge on Navman GPS/plotters, I do like Garmin (last 3 boats and roughly 600+ hours on my old Garmin units) and I know they work. I know Raymarine and Furuno work as well.
Ray does have a fuel flow management system sorta kinda similar to Navman information wise... but I chose to stay Raymarine GPS/Plotter over Garmin this time out and personally decided to go with a dedicated fuel management system (i.e. the Navman 2100). Floscan also makes a good unit as well.
Think I paid $140 for the Navman guage at Consumers Marine (
http://www.consumersmarine.com) and paid roughly $800 for the Ray 435C.
If you do any big water lakes, nearshore, offshore stuff to include fishin,,, you'll definately want a fuel management syst over the "standard get it close" fuel guage. (I dont even trust my Yama guage pack, I do trust that Navman 2100)
I guess it's a personal choice whether to have it built in as a "combo" unit, or to have it as a dedicated guage. For reliability, I chose dedicated units. And weather dictates how yer gonna run, how fast, etc... so a accurate fuel gauge or flow meter is extremely handy, especially if you need to calculate around bad weather to run to another inlet or that type of thing.
Not bustin on ya Macojoe, but I had to chuckle on the fuel comment "$450 is alot of gas for the season!!" man, let me know where yer gettin it at then at that price for alot of fuel!!! that's two offshore trips for me!!! (just shy of 100+ gallons per trip!!!!)

Then again, I guess we dont have to run 40 mph in 3-4 ft. seas either..... My wife would be estatic if she knew only $450 would do it for a season for fuel. So far in the last month the boat has went thru 590 gallons