When I updated my MacBook Air from Mavericks to Yosemite, it was a disaster. I had a XAMPP installation for web-development, and the MySQL (phpMyAdmin) stopped working. This was a widely reported issue. I then understood why Alex Lindsay keeps repeating that he never updates his mission-critical machines. And I became wary of updating my Mac again. So... I'm again getting the temptation / itch to update my mid-2011 MacBook Air (from Yosemite 10.10 to 10.10.3). Do you have any words of caution or advice?