There are a lot of apps that will be replaced -- or at least have some very heavy competition -- from the new features in iOS 5. It's easy to look around the App Store and see developers that have been 'Sherlocked' by Apple's inclusion of their functionality in the core OS; Twitter clients in particular are going to have a hard road ahead, and no-frills reminder apps are pretty much done for.
That's not the same thing as the wholesale borrowing that Apple has done from the jailbreak community with this new version of the OS, especially in the new notifications tools. Obviously, since JB devs tend to focus on new interaction methods and other system-level tweaks that would be off-limits to App Store products, there are more and different ideas about how the iPhone and iPad should work being tried and implemented there. That makes it fertile ground for Apple to see what does and doesn't work, and cherrypick the best ideas for internal use.
That may not be cool, but it's certainly in character for Apple to leverage third-party innovation in OS development, both on the Mac and on iOS. Here are a few examples of some noteworthy 'flattery' from Apple's iOS team to the jailbreak developers who broke trail.
One of the main reasons people jailbreak is to get better notifications and a useful lock screen; both issues Apple has finally addressed in a very big way in iOS 5. A few of the popular lock screen apps are David Ashman's LockInfo and Intelliborn's IntelliScreen, and both resemble (if they didn't inspire) iOS 5's new lock screen. In terms of notifications, Apple's taken aim at a couple of favorite JB apps: Notified and the recent MobileNotifier.
iCloud syncing looks like a fantastic backup system, so much so that EvilPenguin already feels that its backup tool iBye is no longer necessary. In fact, James Emrich, the developer behind EvilPenguin told TUAW: "iBye was a backup/restore manager for content. Basically what iCloud does without auto backups."