I upgraded this morning to Yosemite, and I am quite pleased so far. The look and feel is quite clean, and there were no issues (so far) with the switch from Mavericks.
I had problems with my (now next to) latest model iPad in moving from IOS7 to IOS8 over the air. It got really hosed (the thing seemed bricked, actually), but I got an Apple tech on the line immediately and he got me fixed up via iTunes in short order. I did have to do a factory reset, so there was a bunch of work to do to get my iPad back the way I had it set up. I did lose a little data, but not much. I have not updated to IOS 8.0.1 or 2 out of fear of having to go through all that again. IOS 8.1 is due out on Monday, and I’ll probably give that a go.
But I can recommend the Yosemite update as being pain-free, in my case. You can update a bunch of Mac Apps after you get Yosemite (Pages, Numbers, iPhoto, etc.).