> Is there a benefit or draw back to the IFS system, other then the obvious fact that the lens doesn't change length when zooming?
Internal focus (I assume that's what you mean by IFS?) also means that the focusing helicoid is pretty much sealed inside the lens, so it's a lot harder for dirt and grit to get into it. Not that this is a huge problem, but it's certainly a benefit. An internal focusing design usually has some additional optical problems to solve, and while they usually are addressed in the design, sometimes this shows up in compromises elsewhere. The one place where internal focus may mean a real practical benefit is in a short macro lens - say, 100mm or less. In these cases you are likely to be very close to the subject to begin with, and if your lens extends to focus more closely, you eat up that distance quite rapidly. With the 105/f2.8 AFD for example, the lens extends about an inch from infinity to 1:1, and that can be an issue either for lighting or when shooting live subjects that could get spooked if you (or the giant camera descending out of the sky) gets a little too close. With really long lenses (600/f4?) the elements are so big and heavy that internal focus is about the only practical way to design the lens.
> Why do some of the lenses I see have the VR in red and some in Gold?
Random thought from the marketing folks when the lens was first brought to market? There doesn't seem to be any rhyme or reason to the colors.
> I found some used lenses at a pretty good price, but I am not sure how to tell VR I from VR II?
The only lenses that could possibly be confused are the 70-200/f2.8 AFS, 300/f2.8 AFS and the 200-400/f4 AFS, each of which was available in two different models, one VR-I and one VR-II. All of the others are only available in one model. For example, the 18-200 VR ONLY has VR-II. All of them. (Even though some have different color VR markings. Remember, color is not an indicator of anything.) The 80-400 AFD VR is ONLY VR-I. In practice the only one where there's any thing worth really knowing is the 70-200. The 200-400 is essentially identical with the exception of one additional stop of suppression, and my understanding is that the 300/f2.8 is the same way. The 70-200, on the other hand, has both an upgraded VR system as well as fairly significant optical changes that are unrelated to VR. This is reflected in a nearly $1000 difference in available price.
> 18-200mm would probably fit my needs quite well. ... It isn't much more for the 18-300mm but I don't think I would need it since I have the 70-300mm. Am I missing anything?
No, you're not missing anything. I think you'll find that the 18-200 is a noticeably smaller package, and that its optical compromises are less, well, compromising than the 18-300. I'm pretty sure that the 70-300 will outperform the 18-300 at 300mm, and probably by an interesting margin.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!