The truth is, I'm not qualified to say because I never went up there. But I can share with you what I saw. Actual results may vary, and if you had firsthand experience, please share it in the comments.
The first night of the cruise was the PJ party, and the only night the guys were actually scheduled to attend the deck party. Jordan, Donnie, and Joe came out and security pushed them through the crowd to the stage in the center of the deck. There they stayed, drinking and talking to other people on stage. Some party-goers were allowed to go up on stage as well. I'm not sure how they were selected or who chose them. After a while, Donnie and Jordan climbed up onto the railings of the stage and started singing with the crowd, effectively ignoring those on stage. Joe left first, then the other two departed later (I want to say around 1:30 a.m.?). Since all the action was happening on stage, I don't remember what, if anything, went on upstairs in the VIP area.
Friday night:
Saturday people seemed to expect another on-stage showing, and they were camped out in deck chairs around the stage several hours before the party. Group B had their concert that night (started at 10:30 p.m.) so much of Group A was chillin on the deck. Shortly after Group B got out and made their way to the deck, the VIP party started on the deck above. Behind the rope, a large crowd of women waited at the edge of the party hoping to be let in. Some stayed there all night, and to them it was worth it because sometime around 4:00 a.m. I know Donnie came over and got them all vodka. (This is what I heard secondhand at least, so hopefully I'm remembering it correctly.)
Everyone but Danny made an appearance Saturday night. The highlight, of course, was Jon singing Happy Birthday to Jordan, which was around 3:00. Jon made his way to the stage area for that, so at least the girls who had camped out by the stage for hours got a little something. The pictures I have of the VIP area show it very open (they're all super dark and out of focus though). I see lots of guys but not many fans. Maybe they got in after I left? The telling part is that I only have a few pics of the balcony, but 20+ pics of my friends and me having a great time downstairs.
Once again, there were a bunch of people camped out around the stage and more waiting behind the rope to the side of VIP. Since it was the last night, my friends and I decided to see if we could get in. We went inside to where another group was lined up in front of a security guard. After standing there for about two minutes, I felt pretty grossed out because I could see the guy looking us all over (surefire way to send your self-esteem to the basement). But, we were told we could go in. After going through the hallway though, a female guard at the deck entrance told us to leave. So we looped around, were told to go in again, and again were told by the woman to get out.
That was the end of our VIP experience. It was PACKED on the upper deck, both in the holding area and in the VIP area. People were tripping over each other and shoving in all directions. Trying to get in was, even more than waiting in lines, the least fun part of the weekend. (For one, there's no bar in or near the security line!) We had a far better time Saturday ignoring the VIP area all together. But we didn't waste much time Sunday either.
I have heard people who were in the VIP area say they had a fantastic time up there, and I'm sure if it had been me I would have too! But my advice is, don't waste valuable party time standing at a rope watching other people party. And don't make yourself feel like a piece of meat while some part-time security guard looks you up and down. You'll have the best time if you get down with your girls and just blow a few kisses upstairs.