Bamspeedy
CheeseBob
I feel like the whole razor blade/poisoned candy thing is just an urban legend that got out of hand.
I don't have many curmudgeonly takes on things, but I definitely think we go way too far to protect our kids from stuff like this, or kidnapping, or whatever boogeymen are out there that suburban white parents are using to push their neuroses on their children.
There has been cases of it happening, as shown in my link and snopes even says the razor blades and pins do happen (albeit rarely). Whether that is demented people getting the idea from the urban legend, or it was the kids hearing of the legend and doing it themselves to get attention, I'm not risking my kid eating it if it was obviously tampered with, and I hope you wouldn't let your kids do it either.
That said, my kids don't do the 'house to house' trick or treating (well, the oldest one does now with her friends), our town has a 'downtown business' trick or treating, where the businesses hand out candy. 30 stops by walking a few blocks is nice.