I bought these paper towels recently (not for buttercream, just to use) and when I used them to dry dishes, they left TONS of lint behind.  Don't they leave lint on cakes?  

You must use a crusting buttercream and wait for it to crust before using the viva. Crusted buttercream has a dry feel to it, therefore lint should not stick. 

I have done this numerous times and have never noticed any lint left behind but just like FioreCakes mentioned you must use a crusting butter cream and let it dry before smoothing it with the paper towel.