I recently sold my N80 and will be buying an N73 at the end of next week. However, you'll be surprised as to why:
I picked the N73 over it for basically two reasons: camera, and screen
I'd noticed that I don't take as many pictures with the N80 as I used to with my 6682 and I think the reason is cause it's a great camera, just not a great point and shoot camera. The video on it, I was real impressed (though not low-light, as has been beat to death). The N80 has a bit of shutter lag, leaving most pics slightly blurry cause i'm not a patient person.
The screen, the font on the N80 I personally found a little too small and not bold enough. There's another thread where someone posted a picture of the Text Message creation screen. On my N80, I have trouble reading it with certain themes and in different lighting, cause the letters aren't bold enough to be read. The N73 seems to have bolder text.
Honestly, those are the two reasons I decided to do it.
Build quality, at least on my (Made By Nokia, asian edition) N80, was superb. Battery door didn't move at all. The slide was solid, with a noticable "click" at fully open/closed. There was a little bit of play to the sides, but not visible to the eye, really.
The first firmware out the door sucked, but the newest, not sure what it is, was awesome. I never got out of memory errors and could use Web and Agile at the same time, no problems. Web never crashed on me, battery life was on par with my 6682. I could easily make it through a day.
I think the N80 got a bad rap because the first firmware was buggy. I do think with WiFi Nokia should have put a bigger battery in there, but it was certainly a very usable phone. I personally didn't have much use for WiFi, so it didn't matter to me, But I know it sucked the battery down pretty quick. If I wasn't so interested/reliant on the camera, I'd have kept it, it was an awesome phone, and the screen was amazing. I like the slide form factor, as well. I didn't think I would, but I'm a huge fan. All the benefits of a flip, without the hassle of opening it to do anything.
I'd say the N80 is awesome for entertainment-minded business users.