I've asked Susan Palumbo what was the product she used. She said she used Sol-U-Mel from www.melaleuca.com. She also suggested to try Goo-Gone Professional from Wal-mart. But she said that the Sol-U-Mel is non-toxic and a much better smell.
Also, in other web sites people are suggesting to use Goof-Off (http://www.goof-off.com). They said that works wonders !