The nasty places are the one that are easiest to stumble across,

My old theory about how open clusters are a good place to look for ETI is starting to get a second look. Our sun was formed in such a place, but was ejected (OCs tend to be easily disrupted by galactic tidal forces and old ones are very rare). Apparently, the close proximity of stars in these clusters tends to lead to near-collisions and close encounters, and the solar systems are gravitationaly distorted. Maybe its only those stars ejected from their home clusters early in their history (like our sun) that have nice, well behaved planetary systems.

Statisically this means that perhaps only stars ejected early in their birth cluster's history have a fighting chance of having habitable planets, not systems where the gas giants have caromed through the habitable zones, wreaking havoc. If so, this is not good news for SETI fans, or even the search for any extraterrestrial life.