Here is a screenshot of my very last work: real time quite high quality soft shadows on geforce class hardware, using no extensions.
Basically it is based on motion blurred shadows. I do so to be able to display many shadow volumes at the same time:
do not glclear alpha, do not use alpha for blending. Alpha is for shadows, nothing else, nah!
display shadow in alpha using the usual stencil volume
motion blur alpha
display quad as usually, using alpha buffer instead of stencil buffer
Other screenshots on my web site at:
A demo can be downloaded at http://tfpsly.planet-d.net/Files/demo.zip