Seconding above on not being able to do it on some boards. On the other hand, even here, apparently some people have a trick that makes the mouse-over inop. Don't know how, but it happens.But, if it's a thread you want to check out, just run the cursor over the thread name and you'll get the first part of the thread and can decide if it's something you want to read or not.
I try to make the title intriguing, while keeping it relavent to the thread. More than just "got a question", but more interesting than "got a question about '___'"