I took that screen shot from Engadget’s iOS5 walk through. Twitter integration is nice but look at the top of the screen. A link to install Twitter’s official iPhone / iPad app right from the system preferences. No one will look for another Twitter app outside of the official one. This is bad news for all 3rd party apps.
Also, why didn’t Apple choose Facebook for this integration? Twitter seems like an odd choice compared to the behemoth of Facebook.