My daughter is 3, so my setup is a full child seat, like 86sebring's.
I use just the lap belt of the harness through the bottom of the seat. On top, I went into the trunk and replaced the shoulder harness anchor bolt with a forged steel eyebolt. The child seat's top tether then hooks to this. (Note that I have to remove the top tether from the seat and feed it through the harness opening in the tub from the trunk side; the hook obviously won't fit through a webbing size slot.)
Over the winter, I am probably going to replace the two lap belt anchor bolts with forged steel eyebolts as well. This will let me dispense with the lap belt and utilize the LATCH anchor system built into the child seat. (I'm using a Dorel which has safety-locked J-hooks on the LATCH harness, so they will clip to the eyes. The fancier Britax in my wife's car has some nifty pushbutton claw-type anchors on it, but they are way too small to ever fit the eyebolt.)
And like Lee, we stick to the backroads and generally just go to local cruises. I'm sedate enough with my driving that my daughter has actually dozed off a couple of times. But, try to pry her out of the Cobra and put her in Mommy's car, and it's: "NOOOOOOO!!! I want to ride in the Cobra with Daddy!!!"
