When you're replying to an email, and your email client handily underlines the misspelled words, and you notice misspellings in the message you're replying to, do you correct them?

Is it better to pretend you didn't see them, or just not care, or is it better to fix them, to save the person the embarassment of reading over their own quoted words and seeing their mistakes?

Is there a difference between personal notes and professional correspondence? Does it matter whether it was that the writer didn't know the right spelling, or just totally messed it up via typo?

(I'm not spellchecking this post, just to help the conversation along, btw)