I just found out about the Math Input Panel in Windows 7,and now there is commercial software using it for LaTex writing. For example Inlage. If you have a look of their first demo video, you know what I am talking about: http://www.inlage.com/videos
I had a try with the Math Input Panel myself, and it seems you can basically write all math stuff, integration, super(sub) scripts, tensor, arrows (even with labels over them!), and matrix! The only big problem is there is NO commutative diagram. And it probably has trouble recognizing some math fonts, like \mathfrak or \mathcal. But in all, it really recognize handwritings pretty well. I don't have a writing pad, so I just tried writing with a mouse.
I know there are people taking math notes using a tablet PC. Won't this tool drastically improve the quality of our note-taking? It basically changes all handwriting into TeX files!
Maybe I am too late on this, are there more mature product for such purposes? I think handwriting math could actually be slower than typing LaTeX codes. But one good reason for doing handwriting is because sometimes I just don't like to make math writing into code writing (or something like programming). I would like to hear about your comments. Thank you!