I've had the 2011 MBA 13 inch that has served me faithfully for the past 4 years now. Never had one issue with it. I've upgraded to Yosemite, however a few of the new features are not supported now. Not a huge deal. I've seen some speed issues and the spinning beachball a lot more though. The battery on the MBA is starting to degrade substantially. The "service battery" is now on, and I get a max of 2.5 hours of general use before having to charge it again, so obviously I'm going to have to swap the battery. I'm thinking of retiring the MBA despite it still being pretty quick for most tasks I throw at it for the 2015 rMBP 13. Or should I just replace the MBA battery? My use cases are general web surfing, some light productivity work, etc. The Macbook is not a gaming machine so, I have a desktop for that, so "gaming" performance doesn't really concern me. 4 years seems pretty good considering how much use it has. I just don't want to put money into it if it doesn't go another 2-3. General thoughts?