In response to Aaron Seigo's thoughts about a common branding for the Free movement:
Given the plurality and diversity of the FOSS ecosystem, the branding effort needs a meta-logo. People really identifies the different client-side kinds of computers through the bitten Apple, the flying Window and the "Intel inside" circle. Tux won't work at that level, it's more of a mascot than a logo.
Thinking of it, there's a distinctive visual landmark of the modern Linux/BSD client, and that's the Compiz-Fusion Rotating Cube. See the outline created by the cube borders in this screenshot:
It is immediately recognizable as a Linux desktop. It can be easily stylized, it's modern and dynamic, doesn't resembles any popular logo, and the best: it works as a meta-logo.
The Cube is a container, so it can be mixed with the logos of any other project. Think Cube containing the K gear, Cube containing Ubuntu circle, Cube containing Google's Android...
The unifying appearance of other desktop elements (colors, wallpapers...) a-la Tango icons guidelines can help, but it will never by adopted in a universal enough way. But a single unified silhouette can be put anywhere, doesn't require rebranding of complete products, and is already quite popular and recognizable as FOSS.