Another one worries about ethidium bromide contamination - (Sep/08/2007 )
no matter how, duirng the stain and destaining process, the EtBr is diluted and the amount of EtBr drops on floor is not that much. EtBr will degrade after sometime or under sunlight. Even if some EtBr trace stick on your shoe, it'll degrade soon when you walking around, go out etc etc etc.
It MIGHT be carcinogernic, but compare to beta-mercapto, phonol, chloroform etc, EtBr is not so dangerous. Some people told me that in their lab, they used to handle EtBr without glove, as long as there is no cut in your hand, and EtBr do not enter your body via wound, then it should be all right (but of course, this is not a good practice)
anyway, if you are so scare about EtBr contaminated shoe, try to clean it up with some detergent/active charcoal regularly.
take it easy man!!!