Some feedback: the way you invite and share with others via the web interface does not feel that intuitive. For example, I'm having a hard time understanding when and how you split hotel costs with other users. Also, it would be really nice to get an idea of how much the trip will cost in total per person on the trip page.

I'd also echo the suggestion made by the other commenter about having a dedicated page for each trip rather than having to add an itinerary to your own list of trips each time. That page could be more easily shared and could break down costs for each section.