BlackBerry's App World debuted in early April to compete with iPhone's App Store and Android's Marketplace. I tested it out briefly on a BlackBerry 8830 recently. Since the App World itself is an application, I had to click a few links from the mobile browser before I was able to get it fully installed. After installation, the App World worked as it was intended. Unlike the iPhone or TMobile G1, not having a touchscreen on the BB 8830 meant a slower navigation for me. Also, with the smaller screen, I find navigating through the App World slightly cumbersome. The overally lay out of the App Store worked okay for me and the top rated apps as well as major applications were all readily available.
My biggest complaint about BlackBerry and Apps in general is the lack of memory space to install them with. I installed three to four applications before I was prompted with a message indicating I did not have enough memory on device to continue. Despite the fact that I had a blank 1GB MicroSD card installed, I was not given the option to install apps onto it (online reference). This is pretty ridiculous considering you can install applications on SD cards on older Windows Mobile and Palm OS from years ago. Ironically, the App World itself is an application which takes up some of the limited storage space.
Conclusion: While I am not overly impressed with BlackBerry's App World, it does function as it should. With a growing library of applications coming ahead, it should provide ample mobile application functionality. However, with the applications limited to device storage, it will limit the usefulness of older devices with smaller onboard storage. When compared to iPhone's 8GB or 16GB capacity or G1's unlimited storage potential in MicroSDHC slot, this can make BlackBerry's App World less attractive if a potential buyer is putting more weight in that department.
PS - According to this FoxNews article, BlackBerry App World is off to a slow start.