The photographers are always at the entrance to the two parks, so you can get several photos there. We also had photographers take our photos on the bridge which takes you to the Hulk ride, with the coaster in the background, in the street in front of the Spiderman ride (he asked us which way we wanted to face, and I chose to have Wolverine in the background), and also on the bridge b/t Jurrassic Park area and the Harry Potter area (although I didn't realize until we got home that those photos never made it into my account - I'm still upset about that - so CHECK each day!). We didn't encounter any photographers roaming around Universal Studios taking photos, BUT there were many planned photo ops with characters - the Spongebob shop has regular times when the characters come out and they do photos, we got photos with each of the Transformers characters, and we got photos with the Simpsons. You can also get really cute photos done at the exit to the ET ride. And in IoA, the Spiderman gift shop does photo ops with Spiderman throughout the day.
Add to this all the ride photos, and it really IS worth it. I'm so glad we chose to get the package. The only regret I have is pre-ordering, because I bought an AP and we're going back again, and I could have had more photos taken for free - but I only bought the one-trip package, and I don't think there's any way to change that. Oh well!
I am a "budget" trip planner, and I look for ways to cut corners wherever possible - I can tell you I would have seriously regretted not purchasing the photo package.