For a start, KIS 2010 gets rid of all the viruses and immediately notifies you of any new things coming in and will automatically scan any drive put into the computer (which is good but can get annoying)
It hasnt slowed my pc down at all like some other reviews have said
However. I use a desktop pc, connected through WiFi, and KIS 2010 installs a 'protection' thing to the wireless driver. If you already have KIS installed, then you cannot install the driver, and if you install the driver first then it can cause many conflicts within certain programs.
It took me a long time to figure out that KIS was the conflicting program after days of research and fiddling with my system i decided to uninstall KIS and go to Microsoft security essentials which i know is terrible, but at least it lets me go on the internet
But, I reckon if your doing anything through ethernet then it'll work very well and you will be happy, and it is a lot lot cheaper than any of its rivals