[thelist] why fixed-width fonts are bad (for a client)

[Sarah]

Maybe I am imagining things, or thinking of something similar, but it seems 
to me that someone recently asked thelist for links to articles explaining 
(in layperson's terms) why using fixed font sizes is bad. I've tried 
searching the list archives to no avail. Can anyone point me in the right 
direction to this thread, or if it never happened, suggest a good article 
on this topic?

TIA

Sarah