I also didnt know TripAdvisor was owned by Expedia and is the largest user review travel site with about 25 million unique visitors per month!
When I get a chance I'll have to check it out in more detail
2 new things I did notice so far:
- The entire site layout - color, less clutter on homepage
- Users can plot places they've visited or plan to visit and share with others
I read something about a chat option, but haven't explored that way yet. Let me know what cool things you've discovered on the site.