There is a new Cydia tweak that teaches Siri to display the last five tweets from your Twitter timeline. I haven't quite figured out why it's needed, but a few improvements may make it a more useful tool in the future.
The tweak is called TweetLine, and it can be located in the ModMyi repo under "Sources" in the Cydia Store. Once installed just say the word "Timeline" to prompt Siri to access your Twitter account. She will then show you the last five tweets from your timeline. You will also need the free Twitter app from the iTunes App Store for it to work.
TweetLine is free and only works with jailbroken devices. You can also use Siri to send tweets and update your Facebook status by following the instructions here.