Here’s the script if anyone else wants to play (it also demonstrates how to post to twitter with wget, which may be handy for other automation projects):

#!/bin/sh
MB_POST="http://identi.ca/api/statuses/update.xml
  http://twitter.com/statuses/update.xml"

MB_USER=state your username
MB_PASS=state your password

IZ="$(find Maildir/cur/ Maildir/new/ -type f | wc -l)"
if [ $IZ -gt 0 ]; then
  IZ="$IZ"
else
  IZ="ZERO"
fi
IZ="inbox zero status: $IZ"

for MB_HTTP in $MB_POST; do
  wget -qO- --delete-after \
    --user="$MB_USER" --password="$MB_PASS" \
    --post-data "status=$IZ" $MB_HTTP > /dev/null
done

Update: Fixed script to use any Twitter-style microblog API, and included example URL from identi.ca. Go freedom!

Update: Even better, just post to all of them at once! Also fixed anchor… Despite switching to the visual editor weeks ago, I’m still not 100% used to the convenience of it.