@Clay, FBM and FBX are both implementations of the Facebook mobile website - essentially reskins of m.facebook.com with some added functionality. Since they are using the Facebook feed itself, they're not affected by Facebook security settings for 3rd party apps. FriendCaster is a full application, not a reskinning of the mobile site, and uses the Facebook Graph API to pass data into FriendCaster and back to Facebook. Applications using the Graph API are subject to the 3rd party security settings and when a user selects to block 3rd party apps, their posts won't appear in FriendCaster. Facebook frequently updates their security policies and settings and we've found that some users aren't even aware that they have apps blocked. This is perhaps the most frequent question we have about the application and in most cases users find that those not being shown are at least partially blocked in the "How people bring your info to apps they use" Facebook setting. It's also important to note that in some cases, the Graph API feed isn't in the same order as Facebook proper, so posts may appear at different places in the timeline or may be slightly delayed vs. on Facebook itself.
We don't have separate notification sound types at this time, but that's something that could possibly be implemented in the future.