Thanks Tom, perfect ;o)

Whatever I have to note, is that on my end, capMenu's font-size property purely works. If I make the font larger, it also becomes larger in the forums menu. Adding font-size property to the A tag definition, as tom suggested, works the same way.

It may be really up to your customization. Try to have a slightly unmodified version and test how it works, before trying to understand what you did wrong.

For me it works too ;). It's most likely related to another CSS class inside this area. But that's the issue of customization.

I agree there must be something wrong somewhere with my customisation - but I can't see it yet.

I will keep looking and report back.

The font size defined for td.capMenu affects only non-hyperlinked text in the cell; to adjust the size of hyperlinked text in the cell, modify the font size in the following rule:
.capMenu A:link, .capMenu A:visited, .capMenu A:active, .capMenu A:hover {text-decoration:none;color:#000000;font-size:value;}

IF the font-size is not defined in A elements, then it should work for any text present. At least this is something I remember from CSS structure :)

Yes: if no font-size is specified for .capMenu a: elements, then the links should inherit the font size of its parent (td.capMenu). However, when that fails for some reason--such as in Steve's case--the quick way around the problem may just be ...

either:

1) specify font size for .capMenu a: elements

or

2) if font size for td.capMenu is already specified, explicitly specify "font-size: inherit" for .capMenu a: elements.

Or as written above 3) Analyze the customized code and investigate why it doesn't inherit the font-size property at the time when it should :)

Yes, getting to the bottom of the problem would the way to go to find a solution instead of a workaround. :-)
The font size declared in the a:link rule in Steve's lightillusion.css, which is loaded after his miniBB stylesheet), may be the culprit here.

Yes, if CSS is loaded after, there may come something from here... Anyway, a simple (temporary) solution may also work out.
Thanks for your suggestions!