Can you chime in on your old Mac that you have updated OS X on? And can you tell us how the performance has been? I've got a iMac 2011 which could be upgraded. And my friend has a Macbook Air 2010 which is, I believe, also eligible. I've suggested to my friend that she not upgrade right now. I'm going to investigate a bit before suggesting if she upgrades, hence this post. I'm holding off as well on my computer. Though for me it is less of an issue since I'm ready to buy a new computer. She wants to get another two years or more out of her computer and is just now loving the performance since I upgraded her ram to 8gb.