I'm so excited right now! I have my D90 and it seems a lot better than my other Nikon's in some ways! I mean that you have faster control over shots, and it feels like it is much solider construction! You know, better quality in how it was made! I put a meike battery grip on it, and it feels good, but I'm disappointed in the grip as far as battery life goes. The one I got only had one battery tray and it only holds one Nikon d90 battery, and it looks like you can store a spare memory card in there with it.
The camera is in excellent condition, with very little wear if at all! I'm waiting for the SanDisk 8GB Extreme Pro 8 GB SDHC UHS-I Cards that I bought to be delivered. I bought three of them just in case I might need extras.
If I was to recommend a Nikon for someone's first dslr, I believe I would strongly recommend the D90 as long as they are still making them. You can feel the quality of it in your hands.
Now I'm just starting to use my D5100 and my D90 and I can't say I've used the D3100 to it's top ability.
So I'm not qualified to to do a real comparison between the D90 and the D5100. But I can say that so far I like the D90 a lot better than the D5100, to carry around taking shots with. From what I've heard I think the owners of the D7100 would be able to understand what I mean by the feel of it. It feels heaver, has two command dials, and the LCD screen on the top of it to see and adjust your settings fast and easy. Well at least easy once I get use to it anyway! Lol
Now don't get me wrong. I won't be throwing away my D5100 just because I like the D90 better! Lol I think my D5100 will work awesome for macro shots, or any other type of shooting I might want to do. But I will be primarily using my D5100 for macro, and other shots I'm wanting higher mps for.
But I think I'll be using my D90 for my main carry around DSLR.
[MENTION=11881]Moab Man[/MENTION]
This is the best I can give you on that comparison between the D90 and the D5100 so far. It will be a very long time before I'm experienced enough with them before I could even start thinking about doing a serious
comparison.