Tweet or Post to Facebook or Twitter using Siri
Siri has tight integration with Twitter and Facebook to allow posting to Facebook and Twitter.
This is a huge improvement on the workarounds required before now.
As with everything Siri there are a few ways to prompt him/her to post to a social network.
Post a message to Twitter / Post to Facebook
Siri responds by asking what you would like to say. Dictate your message and send the message.
It’s worth noting that Siri doesn’t give you the option of choosing which Twitter account to post to, instead it chooses the account most recently used on your device.