Been working fairly well between my iPhone 5s and 2013 nMac Pro 8-Core since release. Most know both devices have to be logged into the same iCloud account, yet I noticed my Mac Pro was Bluetooth "auto-paired" on my iPhone and I cannot "Forget this Device". Seems there's a few things at work.
Been able to start an email on my iPhone, wait, click on "Mail" on the left side, then work on that email. If the email isn't saved or sent, it's deleted on both devices. I found the "Maps" functionality the most useful.
Noticed the more I use 10.10 the better it performs. I don't understand how, or if this is a placebo effect, but it seems to adapt the more it's used. One key, after first install wait for the system to finish optimizing; some claim it takes 1-2 days, some a few hours, but if interrupted some claim the system stammers for a few days.