I always use a bag of purchased ice to cool my wort and have never had a problem, and I doubt I ever will, at least not from the ice. First, if I'm putting tap water in the wort anyway post boil, I have no reason to speculate that the water used to make the ice is any less sanitary than bottled water or tap water. Theortetically, I guess we could argue that it might not have been completely sanitary before it was frozen, but we could say the same thing about tap water or bottled water. Secondly, and I know not everyone will agree with me on this, but I saw Alton Brown do it while brewing a batch of beer on the Food Network, dammit! Granted he might be an amateur when it comes to brewing, but he has forgotten more about food safety than I, or many of us, will ever know. If you've seen his show, this guy is downright paranoid about food safety. Although the ice manufacturers aren't freezing swamp water, and bottled water stands as much a chance of being contaminated as the water they froze to make ice (in my book anyway), one could argue that with that flimsy bag, transport, etc, bacteria could be present on the surface of the ice. If you know of a bacteria that I should be concerned with that can survive the temperature on the surface of an ice cube and then survive after being inundated by wort that's just a hair under boiling temperature, then I really don't see the point in even boiling wort to begin with.
Obviously, this is debatable, but the proof of the pudding is in the tasting, so to speak. The expert brewer/owner at my LHBS told me if I use ice to cool the wort, "It will get infected." I didn't argue with him, but question to myself whether this guy knows more about food safety than Alton Brown. Countless batches later, his dire warning has not proven true.