Theres some things floating around out there on the net and research that hasn't been fully and throughly tested.
1) People's gluten intolerances vary. The maximum amount considered by some is a 20 parts per million (ppm) gluten content in a sample. This is often the amount to be considered "gluten free". However, some of us can't stand amounts even that high, and have to make sure that we stay away from products containing any amount of gluten.
2) Many items that are marked as gluten free, aren't made with any gluten sourced ingredients. It makes it easier and the only gluten content will be cross-contamination.
Barley based beer does appear to pass tests that mark it as below 20ppm of gluten, but this can be from interactions in the beer itself. There is an enzyme that is said that it removes some proteins, and this may include gluten proteins, but this doesn't seem to be scientifically proven that I could find.
While this enzyme may reduce gluten protein, it does not eliminate it and people can still have a gluten reaction, thus it's generally safer to completely avoid gluten sourced ingredients. See: http://www.homebrewtalk.com/f164/lazy-mans-gf-beer-187412/
Where some of us had tested beer made with the enzyme.
Because of this, you may be able to make a barley beer that you can withstand, but other gluten free people may not be able to. So consider your audience too.