Does money matter?.
Anyway, for basic work, the less expensive is just fine..
BAK..
Since I'm in money burning mode with getting all the equipment for the camera prepared for some upcoming vacation, it's less of an issue. Ideally I would like to avoid spending money on features I don't need, HOWEVER, I always make an effort to get the best bang for the buck, so would the SB-400 or SB-600 be better in that regard? I have a feeling it would be the SB-600...
The SB-400 can tilt the flash head, but not swivel it. So if you rotated your camera 90 degrees, you wouldn't be able to bounce the light from a SB-400 off the ceiling..
I believe the SB-600 can tilt and swivel the flash head, and it has more power..
I'd suggest the SB-600 if you're going to be taking lots of flash pictures and if you're going to be able to set down your camera bag (at home, at relatives' houses, etc.) without the constant fear of having it stolen..
For extended travel where you constantly have to carry your camera gear, the SB-400 may be more to your liking...
I own the 400 and have used the 600..
The former is superb at indoors bounce flash on my D200 if that's any use - it *nailed* the exposure every time at a recent wedding. Small, unobtrusive, light. The orientation snag for bounce flash never arose..
For your needs I'm sure it will suffice, though of course as you know it lacks some features of the 600 and 800 that many photographers would find essential. But I'm not one of them 99% of the time..
Alex..
The SB-400-600-800 not only work automatically on a D80, they meter through the lens..
Do you use bounce flash? If you do, go for the SB-600. The 400 doesn't swivel, and is less powerful. Bounce flash requires much more power as most of the light does not reach the subject...
Ever since I started playing around with bounce flash on the SB-24, I have been doing so whenever possible, so yes it is important. I guess based on that, I should probably go with the SB-600...

