I am an armchair traveler at best. Actually, I do almost all my travelling through the pages of a book. I enjoyed looking at the variety of sites in this Thing but I didn't feel any urge to pack my bags and buy tickets.
I can see how the various sites would be useful to travellers and to those who want to be travellers. This is a useful sort of social networking. However, everyone's experiences would be different and "advice" should be taken with a grain of salt.
I did find the hotspotr site useful on my last trip to Duluth when I needed a wireless spot to feed my need to be online.
I will need to do more thinking to find a use for these sites with my students. Nothing springs immediately to mind.