It is extremely typographically limiting—and ugly in my humble opinion—to be confined to just plain ASCII, impossible if you write in most non-english languages. Unicode is much better, but it is a huge beast and it is hard to find what you need among the thousands of glyphs it contains. Of course not all fonts are created equal, and they may not contain much more than just ASCII glyphs and a little bit more to keep all us Europeans happy. The Arial Unicode MS font is one of the most complete Unicode fonts.
As I was writing our wedding-info page [Danish] I wanted a “Superscript Three”, as it's called in the Unicode standard, but couldn't figure out how to get Font Book to show me the hex codes for the glyphs—like Windows Charmap and gucharmap can—so I started googling and stumbled upon Brett's Absolutely Astounding Interactive Searchable Unicode Chart, and it is.
Oh, and “Superscript Three” is written
³’ in HTML, like in square-meter,