A GPS like a Garmin is very useful especially if you plan on entertaining guests frequently. At that point it's not just your own life in your hands. Garmin does a great job of canvassing the lake and making continuous improvements to their software. It isn't all-encompassing--having the Bizer map is a great idea as well just to help you keep your bearings and navigate tricky areas.
We were going through what we learned later was the graveyard--planing out at mid-20s cutting a corner of it off accidentally. I was on the front of the boat and started yelling at my friend because I could see boulders right below the surface! We really, really, really lucked out and didn't hit anything whatsoever...But we paid a LOT more attention to all the buoys after that day.
That said, there are a lot of large, uninterrupted areas to cut your teeth on before you start to navigate the trickier areas. I'm a big fan of Sally's Gut and Stonedam Island.
