I too would like to see documented evidence of drive-by spamming. So far, it just seems to be a well-speculated obvious possibility. If this is such a problem and you see it happening as much as you say, write it up. Send it in to SANS or Usenix Security or DefCon or something. I want to see the logs, sanitized if you must, but I want to see them
in a forum where there is some sort of peer-review filtering mechanism in place that weeds out the FUD and marketing masquerading as a "study".
Until then, it's just going to continue to be more WiFUD to me.