I just upgraded to v1.9.0.beta11+59 (from beta 8? - not sure how I can tell after the upgrade) and my css customisation above which makes unread topic titles bold no longer worked properly.
All topic titles were bold whether visited or not.
Instead I now use this:
/* Bold topic titles when unread posts */
.topic-list-item a.title:not(.badge-notification) {
font-weight: bold;
}
.topic-list-item.visited a.title:not(.badge-notification) {
font-weight: normal;
}