This is an open-source QuickLook plugin to generate thumbnails and previews for WebP images. Requires Mac OS X 10.5 or later (but tested on 10.6).
Installation
Go to Binaries and click one the latest attached version, then click "Download" in the top submenu. Unzip it, and put WebP.qlgenerator into ~/Library/QuickLook (or /Library/QuickLook). You may need to reboot to enable it (or open Terminal and run qlmanage -r).
Development Notes
The plugin uses the precompiled libwebp.a (i386, x86_64, ppc; git rev. d757523) located in lib. I build it manually, and haven't yet created a script to build it from sources; patches welcome.