I have a Droid X, which I am about to give to my wife and I am getting a newer Driod. We have been using the google calendar, with great success, for the past few years. This will be the first time we have two smart phones and we want to keep the phone contacts (and email in my case) separate from each other such that they don't download each others to the other phone. Can that be done?
The ideal solution would probably be to try setting up a calendar on one account and then sharing it with the other account from the Google Calendar website. I know this works with things like my office's apps accounts because I can see our shared calendars on my phone, but I'm not positive if it will work with a personal Google account (I'd imagine it might, though). You'd also want to make sure that both accounts had permission to modify the calendar, I assume.
Alternatively, Android will let you selectively choose account data to sync with Google's servers, so one way to do this would be:
This should cause the calendar data from the shared account to sync to each phone, but none of the other data (email, contacts, etc). Then the individual accounts can be set to sync the rest of the data, and will exist separately. You could also choose to have your phone sync email, contacts, and calendar data all from the shared account (if appropriate), while your wife's only syncs the calendar data. Then she can have a separate email/contacts account for herself, or vice versa.
One possible downside to this method, however, is that I believe the calendar account will still appear in e.g. the Gmail app, though it won't automatically sync emails and create notifications (in other words, you could choose to manually pull down emails by opening the app).
My wife and I have been doing something like this for years.
We each have our own separate Google accounts (separate contacts, Gmail, etc.)
We've also done this with our calendars:
(This works just fine on regular old Google accounts.)