No matter how much criticized and reviled, Symantec produces some of the most popular security software out there. Since 2007-2008 when Symantec completely reworked their security products, those products, by any measure, appear competitive with the best. This seems to be collaborated by AV Comparatives naming Symantec's NAV as
Product of the Year 2009, PCWorld naming NIS 2010
Top Internet Security Suite for 2010, and PC Magazine granting the
Editor's Choice Award to NIS 2010.
What I hear most often is what a resource hog Norton is, while I can find no empirical evidence that Symantec's current products significantly impact system performance more than Kaspersky, MSE or AVG. Check
AV Comparatives Performance Testing. Total Overall Score for Impact on System Performance, Kaspersky 193, MSE 190, Symantec 188, AVG 164.
I'd think that if NAV and NIS are really such garbage there would be a lot of credible reviews and test results to confirm this.