I'd really push us to leave the left menu as it is (with some visual separation) and think of the user button as more of a profile page then a place to find features. Where watch star goes is another question.
We had bad performance with iscroll in iOS 4 on the PhoneGap app; I'm not sure I'd recommend using it. Its performance gets worse and worse as your page size increases. :(In terms of fixed positioning the only way to do this reliably and nicely (and then only if JavaScript is enabled) is to use something like iscroll and reimplement native browser scrolling.