I ran into major mouse and keyboard lagging recently and I have tried everything that came into my mind. The last step I did was restoring my latest full partition backup of my Windows drive and the lag was gone. But not for long. Right after Avast downloaded the most recent update the lag appeared again, but then I had a clue so browsing the Avast forums gave me the following post and the hotfix available there:
Avast forum post: ** INTRODUCING **: pre-release version of upcoming avast update (now 4.8.1187) 
However, the weekend is almost over, but maybe I can help some of you.
Happy gaming/photoshopping (at least that are the 2 most used categories where lag is annoying in my case)!
