Erin and I become a bit more tech-savy each day.
This past weekend, I was trying to figure out how Erin and I could use one calendar for our busy schedules that would sync to our phones and iPads, so if I add a dentist appointment, Erin would see it pop up on our calendar immediately, and vice-versa.
Quick disclaimer: You need a Mac and iOS (iPhone/iPad) devices to make this work.
The biggest problem in solving this calendar dilemma is that when you're not married, you have separate Apple IDs that you use to buy your music off iTunes and for your iCloud account. So if Erin adds an event to her calendar on her iPhone, it would only sync to devices with her ID on it. So — the solution!
Go on your iPhone, click settings, then "Mail, Calendars, and Contacts"
Click "Add a new account"
Then un-click all the options it gives you (email, contacts, notes, etc.) and just keep Calendar synced.
If you haven't already, open iCal on your Mac and go into system preferences. Click account, and add your Apple ID.
You're set up now! Now of course, maybe you want to have a shared email address and have all of your combined bills mailed to you, or share the same contacts, but especially after having all of your contacts and emails set up, it's hard to start something new. Using just iCal though is a really simple solution that is easy to implement.
Bonus tip: A lot of people just enter birthday's on iCal, but if you actually go into your contacts (which syncs with iCal) and type that person's birthday in their contact field, it'll put a nice little birthday cake next to their name on your calendar.
After writing this, I have fond memories of my mom writing a year's worth of birthdays, anniversaries and special events by hand on her new calendar each year.