Anybody ever traveled to Chile, Argentina or Uraguay?

I'm traveling to these places on a cruise pretty soon, and wondering what to watch out for, or what not to miss.

Depends what you're into. If you like beaches check out Uraguay's Punte Del Este, it's the nicest beach I've ever been to.
Buenos Aires is a cool city, with nice architecture, cafe culture, and great steaks.
Santiago is also a nice city, with stunning views of the Andes on a clear day. Not sure you'll get much chance to go inland to the Andes, but if you do, checkout Bariloche in Argentina.
Also, I imagine the cruise ship will be going round cape horn, so take some sea-sickness pills. Check out the glaciers while you're down there to.
Have fun.