I just wanted to pop in with a quick note on dog vs. cat products. KAK was correct in that she checked with a vet first about the possibility of using the dog version of advantage on her cats and got explicit instructions on how to do so. This is very important as cats can react differently to certain products that are made for dogs. Some dog products can be deadly to cats, even in the smallest amount.
Be sure to keep in mind that if you are using a product other than advantage to check with your vet first and get instructions like KAK did with her vet.
Never use a product with permethrin on your cats, as it can cause seizures.