[dogscoff]

Most people reckon the special ruins techs (ie all the massive techs) aren't very good but there are a few ppl out there who really like the Neural Net thingummy.

This is unmodded, of course. most mods alter the ruins techs in some way to make them more useful. Proportions even exchanges the ruins techs for ruins tech areas, which give all kinds of goodies, but you have to invest research points as well as just colonising the planet.

As for frequency/ probability, I don't know but I do know it can be modded. Have a look in the game's data files and you'll find it sooner or later.