I am one of the security guys saying that the likelihood for us seeing events like Blaster or Slammer again is very, very low (this shall not be a "call to action" for the criminals…). I think that the measures the whole industry took as well as the increased awareness with the consumer made it very hard to write a highly automated, aggressive worm again.
Well, I just read about a new threat: We have seen more and more cities starting to offer free WiFi for anybody being nearby. The village I was in for my skiing vacation in Switzerland actually offered a free service as well for 30 minutes. Then you had to sign in again. If you did not want to do that, you might pay. It seems, however, that the WiFi routers are open for wormable attacks as well: WiFi flu: viral router attack could hit whole cities