Hi,
Currently using WP 2.2, I experienced some problems reading RSS in thunderbird.
I propose to add a little thing to the function that writes entry title :
$title = html_entity_decode($title,ENT_QUOTES,get_option('blog_charset'));
$title = htmlspecialchars($title,ENT_NOQUOTES);
This thing prevent quotes and double quotes not displaying correctly in thunderbird, but it escapes < and >.