a "happy" virus

[J.A. May]

I was taught that viruses that destroy their hosts or cause them great damage 
are indicative of primitive forms. If this is the case then surely viruses 
would have evolved that benefited their host, possibly by improving life 
expectancy and increasing gregarious activity for example, both activities 
increasing likelihood of infection of others; wouldn't a happy host be a 
better host?
I realise that by its very nature the presence of a virus will be damaging to 
the host, and may well ellicit antibody response, but could there have been an 
evolutionary path around this? Perhaps its allready happened many times before 
and various beneficial viruses have been incorporated into our DNA.
Any references appreciated - I wasn't sure where to start looking.
       
                                             Jake

P.S I'm a second year zoologist, does that mean I'm accademicaly qualified to 
post on this group or do I need to wait until I have some letters to accompany 
my paltry knowledge of virology? ;-)