Seeing that I'm currently hosting three social networks, and trying to be active on all three, I needed a way to post to all three simultaneously. This is the script that I use to cross post to all the places. ;)
StatusNet posting is simply using curl, Pump.io uses the CLI scripts in my pump install and Diaspora is using cliaspora. The script can optionally post to all three at once, a single network or any combination of just two.
For pump.io posting, if you haven't ever used the CLI scripts, you'll need to run the pump-register-app and pump-authorize in order for my script to post (as it uses the pump-post-note script). Also, I am using a version of the pump-post-note script that has a post to Public option as well as a Quiet option (it doesn't return "OK" after posting). You can also see my previous posts regarding posting via the command line here and here for more.
Posting to Diaspora is done with cliaspora. My script will test for an open cliaspora session and will open one if the test fails.
The script can be found at http://bin.jpope.org/crossposting, edit the settings at the beginning of the script and use the flags d, s and p to post to Diaspora, StatusNet and Pump.io. You can also post to a single network or any combo that you'd like.
Just be forewarned, you should likely never cross the streams...