Consider adopting Flickr-style progressive disclosure search options

Overall, I like it. Cleaner than the dropdown. I like how it defaults to 'Search Everyone's Uploads' and doesn't show further options unless you click 'More search types' (i.e. my screen looks different than your screenshot)

But I think it would be useful to watch people (in different 'roles) search, see how they use the search, to inform further changes.

As a counter to this feature I would like to highlight how often normal users do not see these sorts of magic interfaces.

A typical user will click in the search field, look down at their keyboard, type their search query and then press the Enter/Return key, never seeing the drop down.

This is an issue with the search drop down in Commons 2.0, the interface is simply too abstracted.
The above proposed solution is indeed better and technically more capable, but I believe that it will suffer the same fate for many people.

One situation where I was required to provide a similar dual search in one solution I used radio form elements that were below the text box.
In this case there is a horizontal space limitation, but it does provide a clear indicator as to which scope is available.

As another alternative providing the search block as the "Entire site" search only with a link below "More search options" or "Search options" that takes them to a page where the interface can move below the header and into the main content area seems like a good possibility.

As with nearly everything in an interface that has more than one purpose or function, confusion or misunderstanding will be the result.

Better image labels.