First of all, recommend a great news website for the travel and lodging industry: Hotel Marketing
I just found a interesting post at Hotel marketing about TripAdvisor acquired 5 small travel community/content website in a roll this May.
I did a quick check of those 5 sites and following are their Alexa status (I know, I know, Alexa isn't trustworth but better than nothing)
All those websites operates in a biz model like this: some UGC + some Other's content + Ticket/hotel search (revenue source)
My quick conclusion:
1. Content is king for online travel and people trust UGC
2. It's very scattered. So TripAdvisor is trying to consolidate to be the No.1
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