I've just uploaded a Library to be used for attaching an overlay to existing UI elements to allow them to be dragged around via mouse (with ability to scale those frames with the mouse wheel as well). It also, by default, will snap those frames to a 10x10pixel grid centered on the center of the screen as well as snapping to the screen edges if close enough.
I'm using it in a mod i'm working on to overhaul the stock UI but felt a Lib would potentially be useful to others as well. It does still need testing though (hence the beta comment) as, while it works fine in my own usage, its still fairly fresh code.
http://www.esoui.com/downloads/info168-LibDragWin.html