IMO, brush libraries would be much more useful if they could be edited and saved while open in another document. Having to open a library file to update it is NOT a smooth process.
Tell me if I'm missing something.
I'm still using CS5. I assume it's the same in CS6.
I agree. And not just brushes but swatches, symbols, styles, all libraries would be much more useful if they were "live" to a degree and could be updated and edited application wide without the need to save and load external files manually.
(you're not missing anything, nothing new regarding this in CS6)
I can open and edit an InDesign Library in any document. As for "app-wide" or "doc-specific", I don't mind if library elements are automatically added to a document library as they are selected or used, but the inability to update external libraries, on the fly, makes maintaining them cumbersome.