I've just uploaded a joomla 1.5 module to display a share to diaspora button.
The module automatically takes the url of the page, the page title and the introtext and sends it to the users diaspora stream and shares it with their frineds.
I added a parameter to limit the number of chars sent, as I only use the readmore on blog posts and rarely add them to standard articles so posting a full article to your stream could be a bit too much.
Plugin and 1.7 version is on the way soon...
xxxxxx - Update - xxxxxx
Joomla 1.6/1.7 module is ready