When editing an Sweave document in LaTeX (using the Noweb mode), Emacs knows to "ignore" code that is in <<>>= blocks. However, for interstitial \Sexpr{} blocks, this isn't the case. Given that R references by columns via '$' and LaTeX uses $ to set-off equations, these \Sexpr{} blocks often break the syntax highlighting, like so:
I have a very rudimentary understanding the elisp & Emacs syntax highlighting, but my hope is that it might be possible to add something to .emacs that will disable any parsing/$ detection within \Sexpr{}'s.