will the focus becomes better or concentrated on the face when using face detection in the back camera ?

No.
Here is another one with faceblur instead of facedetect and the
backcamera:
gst-launch-0.10 v4l2camsrc device=/dev/video0 ! video/x-raw-yuv,width=320,height=240 ! ffmpegcolorspace ! faceblur profile="/home/user/haarcascade_frontalface_default.xml" ! ffmpegcolorspace ! ximagesink

we need a GUI for all of this nicolai, are you up to that ?

Second that. And don't forget to optify everything possible. I have run out of rootfs space when installing ros-cturtle-base. Had to remove several language files from /usr/share/locale because dpkg --purge anything didn't work when there was no space.

Thankfully, it turned out that File Manager gives status of rootfs clearly. Maybe, I'll get enough patience to wait while apt-get unpacks this archive.

EDIT: How can unpacking be that slow? Slower than downloading? No wonder I thought it was stuck.
EDIT: How do I reconfigure packages? It seems they tried to configure in wrong order.
EDIT: libboost-* couldn't configure itself because it tries to optify non-existent doc folder. I make it by hand now, but developer should become aware of the problem.
EDIT: I don't have a command roscd. What does it mean? Ok, workaround is cd /opt/ros->tab
EDIT: Why does dpkg say "No space left on device" when File Manager displays about 700MB free space? And apt-get knows about this free space, there were about 600MB free space while apt-get was unpacking a large package.
EDIT: I have to install subversion. But I will purge it as soon as possible.
EDIT: I have tried to run make inside gscam. I have taken /cmake.mk from pkg-kde-tools. But now it wants /usr/share/cdbs
EDIT: Ok, I installed cdbs, now makefile wants rospack, it means I have to install whole rosbash (I hope I can uninstall it later, along with cdbs), how can I do it?
EDIT: Help! Why does the whole /opt/ros-cturtle-base folder look like source, not like normal compiled binaries? And it seems that anything you would try to compile here, would require rosbash installed...
EDIT: Purged /opt/ros-cturtle-base, wanting to get deb from site manually. Why does site http://code.google.com/p/ros-n900/downloads/list say its size is 87.1MB (and then the file is corrupted, but it might be problem with Fennec and MicroB), while aptitude download says its size is 91.4MB?
EDIT: After aptitude download the file size is 87.1 MB and it's corrupted (App Manager says so). Help!!!
EDIT: 7MB free on rootfs, 1.2GB free in opt.
Will try aptitude download ros-cturtle-base later, see whether it is corrupted.