Not quite sure what the total number of folks on the web with reduced visual acuity might be, but I consider it semi-significant as most are older folks who managed to accumulate some wealth over the years as well as interests in computers and internet...
And have instructed their browser to use a default font size which overrides your code.
Webmasterworld, for example, works beautifully with a user defined (in the browser) font of 20 up to 28 with no loss of layout, but other sites such as zap2it (example only), have fixed divs barfing oversize text spreading right or display only the north half of letters.
Considering the aging population of folks with money (yeah, I know there are a lot of kids out there but they don't have money, and if economic things don't work out may never have all that much) is resorting to in browser tricks to read what they find on the web. What are you doing to make that possible?
Are fixed width/height divs a thing of the past? (I think so)
Are fixed font sizes same as above? (Should be, screen res makes that essential!)
Are artsy fartsy contrast schemes desired? (Doubt it... browser can kill that, too)
Merely suggesting that among one of many tests we might do with our layouts and designs--and css, too--is to deliberately view the intended output with "old eyes" in a browser set to defeat all font size specs just to make sure the dang thing remains readable! And that other browser setting which kills backgrounds, animations, etc.
At some point folks get tired of hitting CTRL+ to zoom the browser for EVERY FREAKING PAGE they visit. They do the research and discover their browser will do all that work for them from the get go.
Are you coding for that?
Just something to think about.
For example, my default serif font is Century Old Style, regardless whatever "you" (coders) opted to display.
SIDEBAR: Because users can override these settings, keep that in mind when your clients tell you the page just doesn't look right... doesn't look like it looks on a friend's machine, etc. Folks change these settings then forget they did.
All this "not a rant" is a urge toward fluid layout and 1em body text which degrades reasonably in a user modified (enlarged) override.