Now that Yosemite's been out a while, what's the consensus on running it on a 4 GB MacBook Air? Mine runs Mavericks like a champ, no problems. But I read that new security updates require Yosemite, and I don't want an insecure system. My MacBook Air has a 1.7 GHz i5 CPU and 4 GB of RAM. Will it work well with Yosemite, or will my system turn to mush? My backups are on a pair of Time Machine drives, so I think I could restore from Time Machine if there's a problem. Thanks in advance, MacRumor people!