A positive aspect to this is that the variant will usually have a subject line or attached file which quickly becomes well known. Deleting e-mail having the subject line or attachment is a smart preventive measure. This file must be safe because my friends would never give me an infected program. Maybe not expressly, but you don't know where they got the file to begin with. Also many viruses use the 'Address Book' feature of e-mail programs to spread themselves.
Viruses are most common in shareware.
Actually, to the contrary, shareware is very rarely infected. The shareware industry polices itself very effectively and there have been only a few isolated incidents of virus infected shareware being distributed to a vast number of people. I heard the xxxxx virus will destroy my yyyyy. Not physically, not in the sense that you'll have to throw any components into the trash can. Viruses can only wreak havoc on data.