It appears iPhone's RSS reader doesn't like feeds with empty titles. Like mine. An item without a title cannot be clicked. Though I like the little "blub" animation you get when you try to double-tap on something that isn't tap-able.
I had thought Movable Type 3 was helping out by faking a title with the first few words of an entry. I'm not sure if that was ever the case, but MT 4 is definitely leaving the field blank. Other aspects of the MT4 user interface are distinctly unhelpful when entries don't have titles. Are titleless weblogs a dying breed? Do I really have to conjure up a self-important title for every little thing I want to mention on my blog?
Another iPhone RSS annoyance: clicking on the title at the top (inside the blue bar) should take you to the website's home page. That's how it works in the Safari RSS reader on a Mac. But on the iPhone, nothing happens when you click.