I have the 8520 and I can run most if not all of the apps in app world. I even run Pandora. If for some reason you cannot get it to run from app world, go to support (of the app) and contact the support people. They will send it to you via your phone and it WILL run properly. Trust me - I currently have 11 apps I have either downloaded or contacted the support people and they sent it to me. You just have to be a little bit more creative if you really want the app on your phone. As for the 8520...I came from the 8320 and I LOVE it! It took me a while, but it is 3x faster than my 8320 plus 3x more memory, not counting the 35 gb chip you can put in.
