We've visited Universal twice during that time period. Once, it was a drizzly week and everything was a walk-on. It was a fantastic experience, just a bit wet.
Last year, we were there during that same week, and the rains held off. The parks were more crowded, and we were offsite - BUT, everyone rushed to the HP stuff as soon as the parks opened. We were able to walk onto Transformers, Mummy, MIB, etc almost every day. Never waited more than 30 min to ride ANYTHING, including the HP rides. We only rode Gringotts once (our firsts day in the parks, on a Sunday afternoon, 35 min wait), and only rode FJ once (I think that was our first ride that day, only waited about 30 min, the queue was awesome). We never did ride Minions, b/c even at rope drop, the line was never shorter than 45 min. Most days, we left the parks around 2pm, having done everything we wanted to do, and not wanting to deal with the later in the day crowds. A couple of days we went back at dinner time, and the lines were shorter again, though never as short as right at rope drop. The longest lines were for the HP stuff and Spiderman (25-30 min, nice queue), and on our very last day, a Friday, for the water rides. JP was about 30 min (this was after riding a few other things), and I think my guys waited an hour to ride Bluto's Barges. They would have done it again, but it was getting late in the day and we were going to do our shopping and packing and had dinner plans on I Drive that night.
I would not hesitate to book that week again, although I'd like to go just one week earlier. We can't count on being out of school that early though, due to snow days, so we got that mid-June week. I would definitely pick the June 11-15 slot if I were you. The crowds were really picking up our last two days.
