Whitey - 7:10 am on Sep 2, 2011 (gmt 0)
building backlinks as a defence against current and future Panda updates
Tripadvisor is one of the largest SEO platforms on the web, and it's brand is likely 2nd nature to the Google's algo , editors and SERP crew.
If they got wiped out their defence would be to ring Google, as would half the OTA's in the world. So it's unlikely to be a defence strategy. That said, Google decides what it wants, when it wants it, and how it get's it. So when they decide - that's it.
Tripadvisor has been publicly sensitive to Google scraping it's content, and presumably link partners and whatever else it wants for sometime.