One of the few issues with the Nikon D600 is that it has a tendency to get dust spots. See the related posts here (under 'Dust spots'). Some people are therefore wary that the Nikon D7100 might have the same issue.
In this post, I compare what my sensor looks like when I first got it and what it looks like now, after about 1000 shots.
When I got the D7100, the very first frame I took was a shot of the sky, in order to establish a baseline for the presence of spots (if any).
With contrast maximized it looks like this:
I now have about 1000 shots on the D7100. Note: I change lenses frequently, at least once every time I use it. I haven't noticed any spots on my shots. On the other hand, I usually shoot at wider apertures. For testing purposes I took a shot at f/16, which is likely as high as I would ever go for normal shooting (normally I shoot at f/8 or wider).
Here is how it looks at f/16:
With contrast maximized the f/16 shot looks like this:
For testing purposes I took a shot at f/45:
Here is the f/45 shot with contrast maximized:
For reference here is what my Fuji S5 sensor looks like (also at f/45):
I tried to remove the dust using the sensor cleaning function and by using a blower but they did not go away. Anyway, I'm not in a rush to remove them since I don't see them in my shots. However, I plan to bring it to the shop for cleaning after around 2000 shots.
Firefly DSC-2000 Review
Nikon D7100 Hands-On Real World User Review
Nikon D7100 Shadow Recovery
Importing D7100 Raw Files Into Lightroom
Nikon D7100 Real World Dynamic Range
Nikon D7100 Low Light Teaser
Nikon D7100 FAQ and Helpful Links
Nikon D7100 High ISO comparison with D7000, D600 and D700