Rather than sharing an entire monitor, it would be nice to share just a rectangular area. This flexible approach would solve lots of related issues, including "single window" screenshare. For instance, if I'm doing mobile development and I only want to share one or two devices side-by-side. Also, if users could resize the area they share, they could reduce the required bandwidth, when needed, or improve the font size without zooming their IDE.

Personally, I like this better than "single window" sharing because switching apps is as easy as dragging content into the shared rectangular area. In Google hangouts, for instance, it's a pain to switch windows especially during product demos or brown bags that require jumping between writing code and executing it.