I also bought the Tottoos, and used it last week in Washington, DC with my 4 kids. These things are great, and better than anything I've tried before (lots of $$ down the drain...hello, clip on tags anyone?)
Anyways, it rained hard on one day, but the tottoos stayed on my kids hands just fine. My kids all love wearing them. Other people on the subway saw them and wanted to know how to get them. I was thinking that these things are so visible that random people can just spot them, and felt good that if my kids ever got lost, god forbid!, someone would definitely be able to see the info to call me.
At $15, it gave me the added peace of mind I needed for my kids, since I'm a single Dad crazy enough to travel with 4 kids!!
I am reordering for our next Disney trip in July for sure, as my kids love Blizzard Beach!