Hi 16Muddypaws, I upgraded my 2011 Mac Air i7 running Lion to Yosemite. I haven't been upgrading since Lion, because Lion suited me well and was very stabile. However, running iOS8 on all my devices I got interested in the new features Yosemite has to offer. Most notible handoff. Eventhough my 2011 has Bluetooth 4.0LE it is not officaially supported. I followed the instructions to run the terminal instruction and it does indeed work. Handoff is great and the main upgrade driver for me, continue with Mail, Safari and other Apps is really cool. Another thing was finally being able to use Airdrop across all devices. Firstly I did only install Yosemite on top of Lion, but I did encounter a few problems. So I decided to do a clean install to get rid of all stuff I didn´t want anymore. Everything seemd better after it, however, I do encounter the WIFI issues now. Safari is basically so slow, that I am using iPad to browse the web, on my Air is is currently unsuable and realy a pain. I am hoping for a fix very soon. Another thing coming from Lion is that for me the boot-up time seems a few seconds longer. In terms of battaery consuption I would say they are the same or a bit worse, definately I do not have battery improvements which is also a bit disappointing, since I read so much that since Maveriks the OS is more efficient and Yosemite should bring it even further. But besides the WIFI issue I like Yosemite very much, also the UI. All seems much faster and smoother compared to Lion. Currently I think it is only the question when to upgrade, not if at all. Hopefully 10.10.2 will eliminate all bugs. Hope this helps, just my humble answer.
