Ask HN: Do startups need to be scared about patent lawsuits?

Over the past couple of decades, the tech giants of Microsoft, Google, Yahoo, Apple, Facebook, IBM have been building large arsenals of patents for the sole purpose of suing other companies later on. We've just recently seen news of Yahoo attacking Facebook over patents. It seems to be very likely that a startup could unknowingly violate a patent with a new product they develop. Many of the patents that these companies hold are not being used in production, and it would be almost impossible for a startup to do the research necessary to find out what they are. What is the likelihood of a startup getting sued for patent infringement, and what precautions can startups take to protect themselves!