Is the spread of viruses from mosquitoes significant?

[Trond Erik Vee Aune]

Dear all,

I was just talking with someone about the threat of getting viruses from 
mosquito bites. Can for example HIV and hepatitis C be transfered from 
one person to another through such bites? Does any virus use this method 
of transfer as its main route? What is the main difference in viruses 
that are able to use mosquitoes as vectors compared to those that 
can't,are they more stable or just more efficient at infecting a new host?

Kind regards,
Trond Erik Vee Aune