Just get the D300...you know you want it!!!
In all seriousness, I had the D80 for a year and then bought the D300 - love both camera's. I think if you get the D300 your desire to consume information will be much greater than with a D80 that you can slap on "Green Auto Mode" and start shooting away. My little sister was so impressed with my D80 that her husband bought her one for her b-day and I honestly don't think she's ever had it on anything but "A" (kinda sad, actually...but she gets some great pics).
So, if you just want a DSLR but crave an "Auto" mode - then the D80 is your camera. As stated though, the 300 as a "P" mode that handles some of the heavy lifting for you - provided the light is good - when you get in a low light situation and need to make some 'manual' adjustments the "P" mode won't help you out that much.
So, if you are like me and many others on this forum and have a strong desire to learn this stuff to the best of your ability with the time you have to spend on it - then go with the 300. Trust me, you won't be sorry. the 300 is an amazing body and I just leave it sitting on my desk so that I can pick it up and play with during the day when I have a few minutes here and there.
You'll take beautiful pictures with either camera - but if the $$ isn't an object and you are willing to spend even more on glass (whatever you do - don't spend all your $$ on the 300 then go with a cheap kit lens) then you will be a very happy camper.
I try not to think that my primary rig (A D300 w/MDB10 grip + 70-200mm VR + SB-600) is $4000 worth of stuff hanging around my neck, but damn...I sure take some nice pictures with it!!!
So - GO BUY THE D300!!! (I'll go ahead and pimp Cameta here as well - I've bought both my Nikon bodies and a few other pieces of gear from them - great experience, only sell USA gear, will continue to do business with them - don't go surfing on the web for the cheapest 300 body - you'll end up with something that you might not be very happy with)
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-Ken
Nikon D300 / D80