It seems on my stock 1.5.1 installation that if I don't enter a title to a post then the 'comments' link doesn't work.
As an example please see the following entry:
Note the double '//' section - where a title for the post would ordinarily be.
It's not a big irritation, but I figured it's worth reporting. (Of course if I've made a configuration mistake this should be obvious with a little testing and I'd appreciate a friendly flame!)