I just upgraded to Yosemite myself a few days ago.
I bought a SSD and put it in an external case. (Still need to do the transplant surgery on the MBP, but running outboard is reasonably satisfactory in the meantime).
I installed Yosemite on it.
Booted the MacBook Pro from it.
Did a migration to it which took several hours.
Turned on ‘Reduce Transparency’ in System Prefs > Accessibility > Display.
There were a few other little tweaks here and there, but the upgrade was pretty uneventful.
I don’t like the looks of Yosemite, but I’m getting used to it already (mostly).
I had to reinstall all my Macports stuff. If you use Macports I suggest you go through the “proper” OS-Migration procedure and save yourself some trouble.
You’ll need to turn KM’s Sync Macros OFF on your KM7 or KM6 Macs (or both) until you get up to speed.
Memory management sucks on Yosemite in my opinion. I’ve maxed my Mid-2010 MacBook Pro at 8GB and am fiddling with low memory regularly.
I run BBEdit, Script Debugger, Safari, Mail, Terminal 24/7, and I regularly quit and restart Safari.
Bloody Spotlight is using 1/2 a GB of RAM!!!
I regularly run iCleanMemory to free up stuff.
When I was running Snow Leopard on this machine I would sometimes have over 100 tabs open in Safari — and that was with only 4GB RAM installed.
Even so I’m surviving and am glad to have many of the under-the-hood changes in 10.10.4.