I've the same problem as fxdr, on my MacBookPro Retina 13" early 2013.
Main problem is that Continuity works from iOS devices (iPad Air & iPhone 5s) to MBP but not in opposite way.
I already tried to log off and back on in iCloud on all devices, as suggested here by Chris (this topic was one of the first resources I found) without definitive results. On the contrary, it seemed to give me some problems (now vanished) between iOS devices, as they stopped working too. doing it again fixed it
Some more details:
1) both iOS devices work like a charm with my iMac late 2012: first tests were with MBP because I had the chance to update it first.
2) both iOS devices work like a charm with the MBP IF I USE Yosemite BETA that I've installed on an external USB disk. It worked before official release and still works (again tested few hours ago)
3) sometimes, on "normal" MBP, on its own, it starts work or stops without any advice, or works with iPhone but not with iPad or viceversa.
4) It seemed to work when I deactivated FileVault on MBP (Yosemite setup asked for it to activate on first start, while it didn't on iMac, and so I did) but, after some time, it started again to give problems.
5) when I power on MBP with "normal" disk and Yosemite official, if it works, it's not immediate. It starts working after 10-15 minutes. With USB disk and Beta, it's immediate
6) for example, now, with battery at 14% it works from iOS device to MBP only with both devices in both ways, but 30 minutes ago, it didn't in both ways. Powered up iMac and everything works in a flash.
Now, I'm waiting for a call from Apple support. Then, if I can't find a solution, I'll try a recovery. Any suggestions?