The ethical barriers to cloning a human are almost unfathomable and insurmountable.
Even inserting a strand of DNA into a functioning genome in some way (via egg/sperm, at fertilization etc) is very hazardous - at what point do you decide to experiment? and you have to bring a child to term to really understand if you have been successful. we cannot as right-thinking people and scientists condone any line of experiments that require the carrying, birth, and infancy of other human beings as test subjects - yet this would be the only way that cloning as a technique could be improved; this, imho, is an absolute block to human cloning and complete genetic manipulation. at present [url+http://en.wikipedia.org/wiki/Gene_therapy]gene therapy[/url] as practised / as envisaged is much more viable and has fewer ethical and moral hurdles.