Google Calendar – How to Sync Yahoo! Calendar

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 the official directions on how to add it to Google Calendar, it shows a calendar URL in a format that is different than the one you supplied: http://www.tripit.com/calendar/ical/...

Your URL has feed and private in it. It might be due to privacy concerns and only your public events can be displayed.

You could try seeing if there are other iCal URLs for your calendar:
I don't have an account so I can't try it, but this url should take you to where the iCal feed is: https://www.tripit.com/account/login?redirect_url=uhp%2FcalendarInfo