For twitter I have learned that the Intent API exposed by Twidroid is not really nice. Instead there is a small very high level library for Twitter called Twitter4J that I used to build an Android App. Posting to twitter is literary as easy as:
Twitter twitter = new Twitter("username", "password");
Status status = twitter.updateStatus("Hello World");
easy, huh?
I was at one point planing to write an Android Wrapper for this library, that exports common functionality with Intents (like you can start a Service with a twitter.PUBLISH_MESSAGE intent or you can declare your app to receive Intent Broadcasts when new tweets are available for your account) but I did not find the time yet (and also maybe it will be at some point be done by the OpenIntents guys).
Have fun!