photo realistic perspective-depth blur ?

http://www.fontshop.com/fontfeed/archives/tip-photorealistic-perspective/

Is there a way to add photo realistic blur to an image, for example
blurring according to depth field in a photo ? Blur should grow with
the distance from the sharp-focused zone...

Btw, can one do motion unblur in Gimp ? i tried some softwares
like ...with deconvolution filter, but was never satisfied with the
result. forgotten the name of that program !

L