I have my Sharepress set up to "share by default" and "Share all of my Posts to Twitter/Facebook by default" too.
I sometimes send pictures from my phone to by blog via Postie which works perfectly and they appear in my blog when the Postie cron feeds in the email.
But there's no ping out to Twitter or Facebook when the new post is created.
I can edit the post and then share it manually, but it's not automatic when the post is created.
Any ideas as to why it's not working as expected/configured?