There's a difference between "skip the line," and what mromalley wrote. There is a separate line for licensed travel guides. If you have a travel guide you go to that line and just skip the regular line. What Mromalley wrote about is getting into the Vatican early, and that is different. You can "skip the line" with any travel agent at one in the afternoon, and stand in line packed in with everyone else. Skip the line doesn't mean the same as getting in before they open to the public.

A lot has to do with when you are going. I remember having a long layover in Rome and asking the person I was traveling with if she wanted to go into the city and do something. She said that she wanted to see the Sistine Chapel. It was sometime during the winter in the late afternoon. We just walked straight in. There might have only been 4-5 people in there. We just kept taking photos of the ceiling. Every now and then the guard would turn around and say, "no fotos." Then when they turned around and we'd start taking photos for another 5 minutes before they got bored again and would turn around again and say, "no fotos."

There were no lines to skip at that time of year or time of day. You really have to say when you are going.