I reuse my potting soil all the time. But I revitalize it with compost and fertilizer (usually, but not always, organic). If I have a pot of soil I am not using, I dump the soil into a plastic bag, add coffee grounds, egg shells and banana peels, then tie up the bag and put it down in the basement. When I get it back out to use again, I add some fertilizer to it. Seems to work very well for me. Also, if I am concerned about disease, or planting something very susceptible to disease, I sometimes put the soil into the oven and heat it.
