Ah, thanks – finally!

I thought I was the only one getting pissed off with this.

Thanks for this post Philipp, I'd completely forgotten about the <legend> tag until you mentioned it. :)

OK, you really need to add an "edit post" feature. ;)
I just thought that I'd add that you can style the legend tag in any way that you want with CSS like so:

legend {
color: #a00;
font-size: 1.2em;
font-weight: bold;
}