My dad gave me a brand spanking new Nikon FM back in 1977. I was 10 at that time. My first upgrade was Nikon FA which is the first camera with Matrix Metering and first Nikon with shutter priority. This was back about the time I graduated high school but not a graduation present.
I bought myself a Nikon F4 pretty soon after it was released. It was the first autofocus camera for me and I was hooked. Then F100 and F5. My F5 with the AF-S 28-70/2.8 was a graduation present for myself when I got my Ph.D.
Since then... both D1H and D1X and D100 too, then D2X, D2HS and D200. Then D700 and of course D3X and D3S. I do have a D50 that I can't remember where I got it, as well as a D300 that a friend gave me in exchange for a circular polarizer. And I gave my daughter a D40 when she was 3 years old and she still uses it after 5 years. My latest body is a D4S and I am waiting for a D5S and hopefully a D5X that has been rumored.
I still have all of the above cameras in full working order. I have had others but have sold and given them away as they didn't do what I wanted. For example I have two D1X bodies, one with buffer upgrade and one without, I have had a D2H but after a disappointment upgraded it to another D1H. I had a D300S and a D7000 that I have given away to kids of my friends. I had a D40X that I don't remember buying, and for some odd reason I still have the original box and paraphernalia left.
A lot of bodies and 30+ Nikkor lenses currently. My slowest lens is F/2.8 and I only have 4 zooms as I prefer the speed of fast primes. I love the rendering of a few select older Nikkor primes, for example AF 28/1.4D, AF 85/1.4D and AF 135/2D DC, AI-S 105/1.8 and AI 50/1.8 which has the best bokeh of any 50 mm Nikkor to date. These are lenses that I will probably never "upgrade", since the image qualities are unique.