I tried Norton Internet Security 2006 few months ago.
Yes, you are right that it lags your computer. Totally true! But
what for? I just got some trojan, simple keyloggers, basic
programmed virus from a friend (he collects them) and did a scan on
them with Norton. Just 1 second, and the result is shown, ALL
PASSED!!!
I get better protection and virus scan using free scan tools from
online. Luckily, i did not buy my copy of Norton. What a waste of
money it would be.