Great site! Found answers to most all questions and decided to go with the F90BT because of all the support available here.
I love my F90, mostly because I knew what quirks to expect and how to work around some of the others. One thing that perplexes me that I can't seem to find anything written on--at least in the F series--is regarding slight inaccuracy of the nav system. It will help me get to where I want to go, but it's off by several hundred feet. I originally plugged in the unit "temporarily" with the gps antenna tossed up by the base of the windshield. It had a low signal but it did find my location. I then unplugged it and permanently installed it a couple of days later. It's in a E450 box truck, so I ran the gps antenna up to the inside of the box roof and installed it on a piece of sheet metal connected between two of the roof rails. The roof is translucent and it says I have a high signal strength, but when I test the nav going to work or home, it either says I've reached the destination a couple of hundred feet before I get there, or it's telling me to keep going even after I've arrived. My old Garmin C330 was accurate enough to know that I'd arrived at the right street address.
I don't have the VSS wire connected yet, but somehow I don't think that should make a difference given the high signal strenth and no tunnels and that I live in the burbs so there are no high buildings around. I found a thread in the D forums that told you how to reset the 3D control and that allowed the unit to relearn the sat's for greater accuracy, but I can't manage to find anything in the F forums. I've tried resetting the headunit and driving a couple of miles--it did't improve, but I haven't tried restoring factory settings.
Anyone got any ideas? Other than this I'm quite pleased with this unit.