Basically, there are about 21,000 attendees at the festival--20,920 of whom are evangelical or otherwise protestant, and 80 of whom are catholic (most from my last parish). The event itself really is wonderful, with morning worship, talks throughout the day by performers and other youth ministers (many of them taking place in smaller tents), music at various stages, and activities like rock climbing, skateboarding, etc.
What I miss when I'm there is an experience of Liturgy. Rather than just have a "worship leader" play music and read a bit from the bible, I think it would be wonderful to start the day off with psalms read (and sung) monastic style. The big "climax" of each day are the concerts at night (complete with a daily "message" from a noted speaker), particularly the Candlelight vigil on Friday night. I always walk away from these experiences feeling like something is missing, and it is--the Holy Sacrifice of the Mass.
In any event, each year that I've gone with my parish, we brought our youth ministry music group with us. They are a powerful group of music ministers who each have a music charism and a commitment to offer their best in the ministry to which God has called them. After the last concert each night, we would gather as a group in our campground and finish the night off with a prayer service that included music, scripture, and some teaching. Because our music ministers really are quite gifted, each night we would find more and more folks from other protestant communities drifting in to our campsite to pray with us. It wouldn't be unusual for our campsite of 80 persons to host over 300 additional people.
Generally, I led those prayer services (which sometimes used the Divine Office) and had the opportunity to share my faith, teach, and evangelize to people all across the Body of Christ. While I was careful to not overwhelm my largely non-Catholic audience, I preached from the fullness of the Church's Tradition--though generally the focus was on helping teens hear and respond to the kerygma, which is a foundation point for all Christians.
It always made me (and the other folks from my parish) smile when we heard these teens and adults from other protestant communities exclaim, "Wow...I can't believe I'm worshipping with Catholics!" :) I'm not sure what these same folks from neighboring campsites thought the next day when we prayed the Rosary as a group at 3 pm.
Overall, this experience was great for our teens. They were exposed to teens their age who lived and spoke about their faith in Christ openly, and the "messages" that they heard from other speakers were great opportunities to delve more deeply into the Catholic Tradition. I also believe the experience was good for our Protestant brothers and sisters who had an experience, however brief, of Catholics who strive to live their faith intentionally.