Huzzah. My Logged In Conditional Text Widget is now public on WP Extend.
This was inspired by this bbPress.org topic.
The code is not particularly polished (there’s an obvious inelegance in the way the two widgets are coded), so I’ve slapped a 0.9 tag on it. It is working well right now on a live site, so don’t let the pre-1.0 put you off actually using it.