I never had a problem with dust on my D90’s sensor, but the D700 seems to be a dust magnet. Dust will show up as dark spots on light, even colored areas of your photos taken at small apertures. The blue sky in a landscape is a prime example of where you’ll spot dust. To see exactly how bad your dust is, stop down all the way (f/22 or smaller), set your ISO to 200, and take a picture of a light colored object such that it fills the frame. Something like a well lit piece of paper or a wall will work. It doesn’t need to be in focus and it doesn’t matter if the shutter is slow. Now open this file on your computer and you’ll see all the dust that’s sitting on your sensor. Technically, the dust isn’t on your sensor, it’s on the anti-aliasing filter that sits in front of your sensor.
The easiest cleaning option is to use your camera’s auto cleaning feature, if it has one. Unfortunately, on my D700 this does a poor job of removing most of the dust. Don’t bother trying to use a q-tip or lens brush to clean it off – best case, you’ll just end up smearing dust all over your sensor, worst case, you’ll scratch it and need to send it back to Nikon for a costly repair.
The next step is to use air to blow the dust off. Set your mirror to lock up and then use a Rocketblower from Giotto’s (get the large one) to blast it off. Be careful not to contact the sensor with the blower. Avoid using “canned air” or air from a compressor – the former can contain bitterants and propellants that will condense on your sensor, the latter may be too powerful and could cause misalignment. Make sure you have a full battery before you start this – if it dies while you’re cleaning, the mirror will spring back into place and you can easily scratch the sensor or the mirror (this also applies to the swab cleaning).
There may be some dust that resists your first two attempts to remove it, in which case you need to use a wet cleaning. I recommend the cleaning swabs and solution from Photographic Solutions. Make sure to get the swabs that fit your sensor size (full frame or DX). You apply a couple of drops to the swab and then work it across the sensor. Don't be afraid to put some pressure on the swab - the sensor can take it - and you'll need it to get stubborn particles off. After the first attempt, take a test shot and check the results. Don't use a swab for more than 2 minutes after you apply the solution as it starts to break the fibers down, and never re-use a swab once you've set it down somewhere as it will pick up debris. It may take a couple of tries to get all the dust off - be careful not to pick up new dust from the edge of the camera housing as you use the swab.
Overall, this can be a nerve wracking experience the first time you do it, but it's really not that bad once you get the hang of it and follow the instructions. If you’re in Dallas or Ft. Worth, head over to Arlington Camera and they’ll clean your sensor for $60 plus the cost of swabs ($5/each). They’ll also show you what they’re doing so you can do it yourself next time.