If you copy and paste a lot while blogging, either from web articles you are quoting or because you compose in Word and paste in, you've probably run into problems with curly quotes, em-dashes, and other "smart" characters, discovering that these don't always display correctly and may result in odd characters on your blog.
NaughtyWordChars to the rescue! If you're using UTF-8 encoding for your blog, it can automatically convert these Word characters to their plain ASCII equivalents when you save a new entry, or when you load an existing entry for editing (this requires BigPAPI). Sweet!
Note: This plugin seems to conflict with the smilies plugin; when I installed NaughtyWordChars, the smilies bar disappeared. When I disabled NaughtyWordChars, the smilies bar reappeared. Update: A new version of the plugin fixes this bug.