Following is an article describing the results of an independent lab testing various AV programs and recently publishing the results. You can see the rankings and comments for both Mac and Windows AV programs. I'm a believer in using an AV program -- just in case.
Jim Hamm
http://askbobrankin.com/security_antivirus_test_results.html?awt_l=GztAF&awt_m=JlQDVMzh5eP6SL