I've been on the internet since the original Mosaic browser; I remember using "FtpMail" to "browse" the nacent web by sending FTP commands to an FTP proxy by e-mail; I remember when they said the theoretical maximum connection speed over your phone line was 14.4.
What I don't remember is *ever* being infected. It takes a special kind of stupid (or to have friends who fit in that category) to become infected. Trouble is, Windows is the tool for the, well, tools.
P.S. Apologies to any who have been infected for the "special" comment but, seriously, don't click on that attachment that says "AnnaKournikova.jpg.exe". Use FF/TB instead of IE/Outlook if you can possibly do so, and disable automatic everything (loading images in e-mails, JavaScript in e-mails, and so on).
Viruses have affected me in a negative way *only* because all employers now insist I used McAfee or some other bloated virus scanner (here are the stats since the last restart: 92360 files scanned, zero issues detected). Applications which should take 3-5 seconds to start up now take 30-45 seconds, becaus McAfee insists on re-scanning all the configuration files and DLLs that the application uses -- again, and again, and again, and ...
What has caused more loss of productivity -- the actual viruses or the virus scanners?