Yes, but the problem with this is that you can't just enter a stream of text. If I'm in a math class, attempting to take notes, I have to point and click on those apps.

With apps that support LaTeX, I can just type $, start typing math, and type another $ to go back to regular text. Sure, I'll have to type things like \int, but that's still faster than trying to find the integral button in OneNote.

Edit: fix typo.

If OneNote is anything like Word you can use LaTeX notation once you are inside an equation environment (Alt + =).

For example in Word typing Alt + = \int^1_2 \sum^x_(x+1) \ge \sqrt(25)

Would produce exactly what you would get in LaTeX.

You can even copy/paste between applications that support MathML.

Sweet; I haven't yet had an opportunity to use the new equation editor. That's exactly what I want; though.

Look into Emacs / org-mode. It supports literal LaTeX, and exporting full documents to LaTeX, HTML, and probably a few others.

If you don't like Emacs, you probably won't like Org, though.

I recently moved away from Evernote for this reason and the slow client. The one thing Evernote has is the websync and webclient but between Dropbox (latex in text files), Gmail and Google Docs I get pretty much the same functionality.