My only material beef is that I think it could do a better job of flagging possible oversights in your itinerary. "Umm Dave, I'm afraid you don't seem to have anyplace to stay on Wednesday night."
On complicated trips, I actually print out a calendar grid and make notes by hand. It would be nice if TripIt had a month calendar view that let you look at things that way.
But basically I'd like TripIt to flag possible problems rather than have me depend on eyeballing it--even though that works OK most of the time.
The printing out of calendar pages is more for trip planning. TripIt doesn't (and isn't really intended to do) anything along those lines.
I use and love TripIt but only like this:
0. Subscribe to my personal TripIt calendar feed.
1. Book flight, car, hotel, whatever.
2. Forward booking confirmation to email@example.com.
3. Now all those details are in my calendar.
What’s particularly useful is how it handles time zones. Flights seem to ‘just work’, and in the notes for any appointment it’ll tell you the local arrival & departure times anyway.