Here are Yach's tips, in reverse order:

10) Device Specific Features: Yach says applications that offer functionality that's specific to a user's device model are usually more attractive than applications that provide few or no custom features. For example, a local search application that can employ the device's native GPS features to determine a user's location is quicker and easier to use than a search app that requires a user to submit a zip code or the name of a city to find local results.

9) Responsive User Interface: Great BlackBerry applications have users interfaces (UI) that are speedy and responsive to user commands, Yach says. For example, an alarm app that displays a confirmation dialogue window after settings are modified is more effective than one that simply saves changes without notifying the user, because there's no question as to whether or not the modifications were made.

8) Available Offline: BlackBerry applications that use "push" functionality to draw information from the Web or other sources and then save that data whenever the app updates are significantly more valuable than apps that need wireless connectivity to function, Yach says.

"Wireless is inherently an unreliable medium," he says.