UTF-8 Support in the Shell
Even though Apple’s Terminal application has UTF-8 as the default encoding, they did not setup the shell to support it fully.
Mietek Bąk did a good write-up on the steps required to make Terminal (and the shell) fully UTF-8 aware, it also includes a note about irssi (for the records, the default encoding in ##textmate is UTF-8, and we use unicode glyphs a lot).
While speaking of Terminal, let me link to my old piece on how to make ⌥← and ⌥→ do word movement in Terminal and how to make ⇞ and ⇟ move caret (that was the page up/down glyphs).