If you create a post while logged in to wordpress over https, the url that wp-to-twitter posts on twitter is a link to your site via https. This is undesirable if you use a self signed certificate because then users see an SSL error when they visit your site.
Please consider making an option to always post http links rather than https.
Since I posted my feature request to you, I upgraded to a proper SSL certificate so I no longer get the error on this site. However I still think its a worthwhile thing to add for people who are using self signed certs.