Although the system restore option is good at taking a snapshot of your computer and restoring it back, the problem is that if you done a restore and you had a virus on your computer..
It will save the virus along w/the snapshot, so when you restore..you are restoring the virus too. Virus maker's took advantage of this, that is why most people like me just shut it off.
Viruses are getting smarter and can travel from partition to partition, so it's good to have a very good Anti-virus protecting your computer. If you do have a very good Anti-virus program, then the system restore option works.