The profession version used to allow you to install it on 2 seperate computers so that used to offset the price a little if you had multiple computers.
I perfer NOD32 myself. Small footprint, very few resouces and extremely fast.
Some people dual layer running 2 programs at the same time. NOD32 and Kaspersky I heard work well together. There was a program posted http://www.extendiaavk.com/
that uses 2 antivirus engines. Its ok but even thou it doesn't cost anything extra don't be fooled into getting the suite .. All the extra programs are pure crap and pretty worthless .. Its no wonder they are giving them away .. Its nice concept for the 2 scan engins in one package but I need to do more testing before I'll recommend it. The scanning is VERY slow .. It uses an old version of the Kaspersky as one of its scanning engines. It would be better is they upgraded to the newer Kaspersky engine but I don't see that as happening.