I stumbled upon Petri Leskinen's blog (http://pixelero.wordpress.com) and a very cool metaballs demo he did with pixelbender. I tried to port this to GLSL and here ist the result.

Meanwhile the image kernel developed into a parametrised Quartz Patch that I use in VDMX as a image source. It looks very nice when thle blobs move to the sound. In the right video you can also see what happens if you skip the Blinn-Phong Shading and use an animated texture instead.