Why are iMacs so sluggish after downloading Yosemite?

[iMore Question]

I have a 2008 & 2011 iMac. Both had Mavericks before I upgraded to Yosemite.
I noticed in my Activity Monitor that I am getting "Google Chrome Helper not responding" everywhere. I noticed quite a sluggish response launching from window to window.
What is causing this and what can I do to remedy this problem?

 

[qbnkelt]

I have a 2008 & 2011 iMac. Both had Mavericks before I upgraded to Yosemite.
I noticed in my Activity Monitor that I am getting "Google Chrome Helper not responding" everywhere. I noticed quite a sluggish response launching from window to window.
What is causing this and what can I do to remedy this problem?

Although I haven't got an iMac, I would imagine that certainly in the case of the 2008 machine it would have to do with the age of the machine. I can't imagine that it would be optimised for an upgrade so many years later. What kind of sluggishness are you experiencing? Specific programs?

 

[HankAZ]

My wife's 2011 iMac (21") is fine with Yosemite. No sluggishness, no problems whatsoever.