I constantly shoot in dusty, dirty conditions. Both the D700 and the D300 are set to clean the sensor automatically upon turning on, and again upon shutdown. In addition, I use a rocket blower any time I change lenses.
In addition, both bodies get serviced by Nikon at least every six months. This includes a sensor cleaning.
I let the pros do the serious sensor cleaning. The bodies are in for the once-over, anyway.