If the stuff is in tripit, you can just add your tripit calendar to iphone/ipad/mac/google calendars, etc. I've tried other methods, and that one is the best for me, but none of them are perfect. For example, the timezones are sometimes screwed up using this method. (try to use "automatic" in tripit, when you can, but it's still not perfect. You will see.)
tripit has device/program specific instructions. They refer to this method as "subscribe to your calendar feed". and they have links to "get your ical feed". As you update things in tripit, your updates will flow to any device/program that subscribes to that feed. (Some devices/programs update more frequently than others.)
http://www.tripit.com/uhp/calendarInfo
If you are just tracking flights, then tripit stuff of course flows well to the flight track pro app. But hotels and any other stuff doesn't, so you still need the ical feed in the native calendar apps, and you probably want them in google calendar or in your mac's calendar app anyway. All of those programs and outlook also all support subscribing to an ical feed. And you can even import google calendar, etc into your i<idevice> using google's ical feed as well. I think its better to maintain your calendar in the cloud rather than trying to do it on one machine, but I suppose that mobile me attempts to do the same thing for those that want to pay for mobile me and keep their calendars locally. I use google for that.
-David