ADAM STOP READING THIS THREAD NOW.
I remember seeing something about this on Mythbusters and I think that it doesn't matter where you keep your toothbrushes because even the control toothbrushes that Adam and Jamie used and kept in the kitchen had fecal coliform bacteria on them.
Here's the video of their experiment:
http://dsc.discovery.com/videos/mythbusters-surprise-toothbrush-minimyth.html
They don't control their experiments well. If they were brushing with the brushes in the kitchen immediately after using the ones in the bathroom they could easily have cross-contaminated them. It doesn't necessarily disprove the notion that fecal coliform gets into toothbrushes from toilet spray.
Or if they used the control toothbrushes in the kitchen first, they already had fecal coliform bacteria in their mouths or on their hands. They did have a Ph. D. and M. D. microbiologist assisting them with the experiments,
Dr. Joanne Engel from UCSF, and I think she would be familiar with cross-contamination and aseptic technique. I know that it was drilled into me in the microbiology class and lab that I took.
The point was that fecal coliform bacteria are an unavoidable part of daily living, but at the low levels found on all the toothbrushes they do not represent a health threat.
I think that it's a good idea to use your common sense but it's also impossible to completely avoid fecal coliform bacteria because they are almost everywhere.