I owned a D5100 for about a week before exchanging it for a D7000. Unless you seriously get into photography, you'll probably get the same quality of photos from either body.
To me, the main benefit of the D5100 is the swivel LCD screen. It helps a lot if you do any type of videos of yourself (such as you doing like a howto video or talking about your tank).
The benefit of going with a D7000 is the body is a bit sturdier, but it does make it heavier. This isn't really a big deal when taking pictures, but the weight does start to feel heavier if you're doing any type of extended video recording while holding the camera (not on a tripod or monopod) in your hands for 10+ minutes. Another thing I like about the D7000 over the D5100 is the body is a bit taller. I feel my grip on the D7000 is much better because of the extra half inch or so.
One of the major differences between the cameras is the type of lenses you can use for autofocus. The D5100 can only autofocus with the newer style AF-S lenses, while the D7000 can autofocus with both new and old lenses (the entire back catalog of Nikon lenses, basically). I believe most, if not all, new lenses being produced are AF-S, so it's not too big of a deal if you only plan on buying brand new. It is nice, though, having full access and functionality from older lenses, as you can buy them used and will produce images just as clear, and sometimes better, than the newer models. You can use the older lenses on a D5100, but you'd have to manually focus by turning the focusing ring on the lens itself.
With that said, the lenses are really what make the camera. The D5100 and D7000 are very, very similar to each other, so your lens choice will have a greater impact than the body you decide to go with.
