I have noticed a slight slow down. Not enough to be a bother.
Dell Inspiron, Win7x64 SP1, Pentium Dual-Core, 6 GB Ram, Avast Free 2014.9.0.2014 beta, Comodo Firewall 5.12 w/D+, MalwareBytes Premium v2.0 RC 1, MCShield, Super Anti-Spyware Free, SpywareBlaster, Bitdefender TrafficLight, OpenDNS Premium, Keyscrambler Personal, PrivDog. CCleaner, Greenshot, Firefox (latest build) and, Google Chrome (latest build).
When you do something, do it with a purpose and do it on purpose.