Thanks for getting back to me so quickly.

@guido: is that what you mean? -> http://iem.at/~zmoelnig/GEM/blur.png

Not really, it looks like [gemframebuffer] has a weird black pixel border all around the edges. 
http://img717.imageshack.us/img717/8998/osxfastblur.jpg

This has something to do with osx, please see the patch attached.
http://www.mediafire.com/?tw3jb9o0ac9fq6i

Best,
Guido