Whole system crashes have been much more common, especially ones related to sleep (the system won't wake up). About half a dozen to a dozen times since the upgrade (one month) but really, there shouldn't be any.
I'd upgraded since Leopard/Snow Leopard it had always just worked for me. Yosemite though had crashes and hanging - I decided a fresh install and it's been working great since.
Not the best news if you're used to upgrading but for me it worked wonders.
Agreed. I don't want to have to worry about shit like this. When I use Windows I would ALWAYS do a clean install and almost always do a clean install every few months because I run my machines hard (installing tons of stuff to try out then removing it). With OS X I didn't have to worry about this and have saved a TON of time not having to rebuild my computer with each release. I expect better from Apple.