Cool idea. Since we're talking trivia, here's a shameless plug for my own app: (Android only) <a href="https://market.android.com/details?id=com.mod0.pubtrivialive" rel="nofollow">https://market.android.com/details?id=com.mod0.pubtrivialive</a>
One issue is that from the question screen there seems to be no way to get back to the categories. You can get a new category list, but not the one you came from.