Check this out - Firefox 2 spell checks as you type
your emails, or, in this case, my post for this afternoon. We wouldn't have a clue we misspelled something if it weren't for spell check; and as a result, we know the need for spell check.
No need to run a separate function to get your email or other web content spell checked... Of course, it doesn't catch when you use the wrong form of the word (i.e. your vs. you're, etc.), nor is the list of suggestions the word you're looking for, but it's so easy for us, we're in love with this new functionality.
If you use Firefox and it hasn't prompted you to upgrade yet as it did for us, seek it out, because it's really worth it. And if you still use another browser, consider using Firefox when emailing or adding content to the web.