I use a lot of technical terms and made-up abbreviations when I jot down notes in Stickies. This causes the spell checker to underline more or less every word in red, which is annoying. Luckily, there is a way to permanently disable spell checking, for all notes. In retrospect, it is really, really obvious how to do it, but it took me a while to figure it out.
First, make sure spell checking is disabled for the current note, using Edit » Spelling and Grammar » Check Spelling While Typing. Then, mark that note's settings as the default, using Note » Use as Default. (This will also set the note's color and font as the default.)
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091127084855131