They are shown in search engines, they just have very little optimization to not be showing as high compared to their dot com and alike counterparts.
Example search of .TO for "shopping"
http://www.google.com/search?hl=en&q=site%3A.to+shopping&aq=f&aqi=&oq=
I would prefer using .to as a hack (come.to, ours.to, and some others) rather than promoting a product to Tonga and the rest of the world. Although their official language is Tongan and English, you are only marketing to 100,000 people-- and I doubt many of them use a personal computer.
With your example above; shop, I would like the domain Shop.At over Shop.To.