The F3/MD4 combo is a beauty. It's dense and durable and inspires confidence the way a hammer does. It is quite heavy, something like 2kg all dressed, but that extra weight is a helluva damper for camera shake. I could hand-hold mine at 1/15 on the regular, 1/8 if I got my breathing just right.
I can't see a reason to own an F4 in 2012. The AF is pathetic, it's plasticy-feeling for an F, the ergonomics are strange, the viewfinder is a hellscape of information overload, and it somehow manages to feel even bigger than it actually is. Matrix metering is great and all, but the only time I see a need for it is when shooting quickly, a situation in which you would also want an AF system which can track a moving object—something the F4 can only do in lab-ideal conditions.
Everything about the F4 screams "stop-gap"; it's not really an MF body, it's not really an AF body, it's not really traditional ergonomics, it's not modern ergonomics. It's the middle child of Nikon history, neither here nor there.