Google Calendar – Merge Multiple Calendars

There's an article on this here. I've not checked that it works, but it seems pretty straight forward. The essence is that instead of importing the calendar, you add the URL of your event feed as a public calendar - here's a summary of the steps:

1. In Facebook click on "Events"
2. Click on "Export Events" and copy the URL
3. In Google Calendar go to "Add" under "Other calendars" and choose "Add by URL"
4. Paste the URL you copied from Facebook and click "Add"

[Update: to make answer more complete]
If you run into issues with private events not showing properly then check out eventbusyfix.info. This site acts as an inbetween to clear the private flag and enable Gmail to show them properly (Thanks to prestomation for this tip)
[/Update]

Hope that helps!

According to Google's support docs, it's not possible to merge accounts.

They do offer a comprehensive list of how to move and share data between Google accounts. For the specific products you mention:

• Google Reader can export feeds from one account and import to another
• Calendars can be shared; if you have meeting invites being forwarded via email you should be able to accept them on the new account.
• It is possible to unlink a YouTube account (by visiting this webpage) from one Google account and re-link it to another (by visiting this other webpage).