just over a week ago I traded my D5000 for a D80 and it was the right choice for me as I only needed a camera and was missing the 2nd lcd screen from the D50 & 10d I had and of course the focus motor widens the lens choices.
you have to really choose them as different cameras, you cannot compare the 2, D5000 has a great liveview with really good LV focus, HD recording which again works quite well, shares alot of the inners of the D90 and is compact and light. it is a very popular choice in camera.
the D80 is bulkier heavier with 4 year old tech but as mentioned by others a damn fine camera, I certainly prefer it as I relate better to the 2nd screen and didnt need liveview or recording and I prefer a bulkier heavier camera.