The qc-usb-messenger ebuild installs, and the driver gets loaded. Then happens the same story: camorama more or less shows the video (hangs on the first start, then I kill and restart it and it works). Xawtv gave the same error as you posted.
I would be interested in using it with skype, but it is not detected there (only microphone). There are descrbed some possible workarounds with gstfakevideo, but when I try to compile it from http://gstfakevideo.googlecode.com/svn/trunk/, there is the following error:
Looks like it wants the 32-bit gstreamer (I have a 64-bit system), but seemingly there are no ebuilds for it/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../../x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../libgstreamer-0.10.so when searching for -lgstreamer-0.10
/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../../x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../libgstreamer-0.10.a when searching for -lgstreamer-0.10
/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../../x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/libgstreamer-0.10.so when searching for -lgstreamer-0.10
/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../../x86_64-pc-linux-gnu/bin/ld: skipping incompatible /usr/lib/libgstreamer-0.10.a when searching for -lgstreamer-0.10
/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lgstreamer-0.10
collect2: ld returned 1 exit status
make: *** [libgstfakevideo.so] Error 1
Maybe we should get something newer that would work with UVC
