Very easy to customize the tooltip within your posts or pages.
I just had one issue and that is that the author didn't say where to find the functionality. But I found it after a while, you have to scroll down in a post or page and then you find the fields.
Great stuff. You can even replace the
<a href="...</em> with
<span class="whatever" so that the tooltip word doesn't become a real link(which is often annoying for non technical visitors.)
The class whatever then can style the tooltipped word to make clear it has a tip.