Measure tool / Info panel does not show area for for many things
Recently Measure tool started to calculate are for selected / clicked objects, originally requested here: http://illustrator.uservoice.com/forums/333657/suggestions/33527584
However, it’s very basic.
1. It does not show an area for objects with no fill
2. No area for objects within a clipping mask
3. No area for the visible area of a clipping group as a whole
4. No area for an opaque raster image (not that hard to multiply two values)
5. ...or for a partially transparent raster image (again, we can evaluate this manually, by using a fill + Outline Object trick)
6. Nothing for meshes, live text, symbols, compound shapes...
Finally, the Info panel requires you to pick the tool to start showing the area! Perhaps you should just show the area at all times?

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Sergey Osokin commented
It's a good start, but the Measure Tool has very limited capabilities right now, not considering Illustrator's many kinds of objects. Also, why would we want to see the area but not be able to copy it or place it immediately with a text object next to the object like the Dimension Tool does?