Q:

Does the use of the fieldset HTML tag have meaning beyond grouping forms?

Usually, I've seen it with forms, but I've found it helpful to group related sets of data (eg when you have multiple tables on a page, using a fieldset around each table or group of related tables to define a visible meaning and a group name (legend)). Is this abusing the fieldset tag to the point where, in my uses, it no longer has semantic meaning?

A:

I believe this would be abuse. http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.10  states "The FIELDSET element allows authors to group thematically related controls and labels".

A:

The "field" bit in the name fieldset refers to <form> fields.
Using fieldset outside forms to group aribtrary data is clearly semantic misuse.
However, your HTML will validate and God will not Kill a Kitten.

A:

fieldset is about form control group. By grouping related form controls, authors can divide a form into smaller, more manageable parts, improving the usability disaster that can strike when confronting users with too many form controls.
That does not means a fieldset always group fields within a form, even though the specification discuss fieldset only within the context of user interacting with form...
So the "abuse" can come from the fact the HTML 4 and XHTML specs do not require fieldset and legend to be contained within form elements. FIELDSET can even be the child of the BODY element. It's valid syntax to put fieldsets outside forms.
But, when you describe something as a fieldset that isn't really a fieldset, you just cause confusion.
It's best to think of HTML / XHTML tags as describing the meaning of an element rather than how it will look. Then you can use CSS to make the element look like whatever you want.
If you group data for presentation purpose, you can find here a nice CSS alternative.
For reference:
.fieldset {
border-right: 1px solid #75736E;
border-bottom: 1px solid #75736E;
border-left: 1px solid #F2F0EE;
border-top: 1px solid #F2F0EE;
padding: 10px 3px 3px 3px;

}

.outer {
border-left: 1px solid #75736E;
border-top: 1px solid #75736E;
border-right: 1px solid #F2F0EE;
border-bottom: 1px solid #F2F0EE;
width: 200px; /* CHANGE THIS FOR BOX SIZE */
} 

.legend {
float: left;
margin-left: 15px;
margin-top: -8px;
padding-left: 5px;
padding-right: 5px;
font-weight: bold;
background: #FFF;
} 

<div class="legend">Lipsum.com Is The Best</div>
<div class="outer">
<div class="fieldset">Lorem ipsum dolor sit amet, consectetuer adipiscing elit. 
Donec congue fermentum metus. Quisque vel ante. 
Cras purus metus, dignissim at, luctus et, sollicitudin eget, urna. 
Maecenas eget lacus. Aenean bibendum risus non erat mattis semper. 
Aliquam placerat nibh eget lacus. Sed blandit eleifend justo. Nam elit. 
Fusce feugiat orci id eros facilisis laoreet. 
Integer vestibulum condimentum purus. 
Proin vehicula congue lacus. Quisque placerat diam nec enim. 
Nunc lorem. Maecenas nec sem sed nulla tristique faucibus.</div></div>

