Most definetely a problem if you shoot regularly with small apertures (high f numbers), as in landscape photography. My D7000 was quite similar to that condition, but using a good hand blower cleaned most of the stuff - not all.
My own testing for dust involves standing close to a white wall, selecting manual everything, closing the aperture as much as possible, focusing for infinity and using low ISO to make sure with an exposure time of around a couple of seconds the whites will be whites. No need for bright lights, just an indoor wall. Then, click the shutter and move the camera in circles during the exposure, to make absolutely sure the white wall is detail free and completely smooth. Then, import the pic to lightroom and adjust contrast curve to make the dots really stand out.
Kind like taking a long exposure landscape pic with lots of sky and seeing a huge amount of "birds"!
I've tried cleaning the sensor myself with a vacuum/wet/dry kit, but results weren't perfect, even after a couple of repetitions. The blower and five or six "system" sensor cleaning cycles got it to an acceptable degree (only a few spots to clean while processing a normal landscape pic).
This is quite annoying, since now I tend to limit myself to shallower DOF pics...
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