I do have d5100 and I confirm that there is no DoF Preview button. You can read about it's purpose here http://www.kenrockwell.com/tech/dof-button.htm
If you really need this button d7000 have same sensor and does same quality photos. It allows for more control using physical buttons (in d5100 you need to use info menu to set some setting). It is also better suited then d5100 for manual lenses. That said it is also more expensive and heavier(but is also more water prove).
Personally most of the time lack of DoF preview did not bother me because I either wanted as much in focus as possible(for landscapes), or only person in focus which was quite easy. Weak support for manual lenses on the other hand baited me once with out of focus picture that I did not notice until it was to late(if it is really bright outside is hard to see photo on LCD, so i just checked histogram).
You can see my d5100 pictures here https://plus.google.com/100147104412340662455/photos if you are interested.
Great, will read through the article and play around to see what the option does on my brothers Nikon D60 (I've been playing around with his camera before deciding whether to splash out). Great pictures, looked at them briefly, will look at them properly tonight. Thanks.
