So much for Handoff being useful. My wife and I use the same iCloud account because we use the same contacts and calendars.
Apple needs to allow a device to use different iCloud accounts for different features.
My wife and I do this with two separate iCloud accounts, and everything works great. Here is how we have things set up:
iTunes Store: we use the same Apple ID (I actually have a 3rd account just for the store, but just use whatever Apple ID you normally shop with here). Note that this does not need to be the same ID as your iCloud ID. My wife and I and both of my daughters use the same Apple ID for the Apple Store for all of our devices.
iCloud: my wife and I each have our own Apple ID.
For contacts, I turned off iCloud contacts on my wife's iPhone. I then added a second (secondary) iCloud account on her phone, and added my Apple ID. This iCloud account has "Contacts" synching enabled and everything else disabled.
You add a secondary iCloud account by going to Settings --> Mail, Contacts, Calendars --> Add Account. On the next screen, choose "iCloud" as the account type that you want to add. Note that you only need to do this on one of your devices (i.e. you could add your Apple ID as a second iCloud account on your wife's devices, or vice-versa).
With the secondary iCloud account, you can use it to share Contacts, Calendar, Reminders, and / or Notes.
To share our calendars, I just share the Calendars I want to be "joint calendars". You can do this in OSX, or right from the Calendars app in iOS8 (click on Calendars at the bottom, click on the circled "i", and then click on "Add Person" to share). I have one private calendar that I use to schedule events that I may not want my wife to see (surprise birthday dinner, etc.).
If you don't mind the calendars being identical, you can just enable the Calendars synching on the secondary iCloud account.
There is one thing that we lose by doing things this way. I wish I could share the Photos on this secondary account so that our photos would always automatically show up on each other's Photostream. I don't know of any way to do this without sharing Apple ID's.
There is also one "bug" / "feature" with my setup. The concept of "me" is stored in the contacts. If you share contacts in this way, your iPhone will think you are both the same person.