Removing dust spots in Camera Raw
You can remove minor blemishes using the Retouch Tool, renamed Spot Removal Tool in ACR 5 under CS4. It replaces blemishes with ‘clean’ pixels from elsewhere in the image.
It’s very useful if you have multiple images with identical blemishes caused by dirt on the lens or dust on the sensor: you can open all the shots in Filmstrip mode, remove the blemishes from one image then apply the same edit to other images using Synchronize.
However, note that if you remove a spot from a clear sky in one image and apply the edit to another image in which there’s detail under the same spot, that detail will be blurred.