Not being a cookie monkster myself I'm not sure, but does the browser know to return the cookie to the www host?   That is, how does the domain and path information get filled in when you don't specify anything?   If the cookie isn't associated with a particular domain, will it be returned to all domains?   Just wondering...

Update:   I'm starting to find references that the domain defaults to the "domain of the document".   I _suppose_ that's believable ;-)