What is the contribution of viruses to the evolution of mankind?
The processes that control the germline of metazoans (multicellular animals) are highly regulated compared to single cell bacteria and eukaryotes as well as plants.  

At this point there are no clear stories of gene transfer into a complex animal, though there are some for plants:

"animals and fungi seem to be largely unaffected, with a few exceptions, while lateral gene transfer frequently occurs in protists with phagotrophic lifestyles, possibly with rates comparable to prokaryotic organisms."

Bacteria fungi and plants are more permissive and more susceptible to gene transfer and it probably is more important to their evolutionary path. 

Its been estimated that as much as eight percent of the human genome has been affected by viral integration.  But viral genomes are highly selected against carrying non essential material - other genes rarely come along for the ride it seems.  What is probably more influential is that viral insertions could participate in rewiring the regulatory network of animal cells, not adding genes, but modifying the conditions under which they are active.