Sometimes, it seems that minor features are able to draw a clear difference between a regular desktop and a highly-usable desktop, latter that contains worked-on-detail elements, in order to immediately familiarize the user with its features and intentions, as well as removing from the experienced user's shoulders the burden of double/triple-checking certain actions.
Unity can be easily described by the above-presented highly-usable desktop, progressively incorporating new and new design-wise details.
The Trash icon is displayed on the Unity launcher by default, connecting a USB stick to the computer, adds its icon to the Unity launcher; yet, opening the Trash (by clicking on its Unity launcher icon) and/or a USB stick (memory card, etc,--storage devices--), exposes their Unity launcher icons as inactive, meaning, their icons remain insensitive, not being highlighted similarly to other icons.
Consequently, especially when having multiple icons on the Unity launcher, the user may be confused about having or having not opened storage devices, Trash, etc, due to their inactive icons.
Moreover, the mentioned inactive behavior creates an unpleasant visual contrast on the Unity launcher, generating an inconsistent unfinished look & feel.
The latest updates landed in Raring Ringtail (via the regular updates) introduce a fixed behavior for Trash and storage devices, in the sense of highlighting their icons, after the user clicks on them (thus opening them).
The result: Trash, harddisk partitions, USB sticks receive a noticeable light, making them immediately visible on the launcher; closing the Trash (after being opened and illuminated), closes it and removes its illuminated icon state.