I have heard that Google doesn't like them at all. However, I am not sure whether they actually take action or not.
At times Google may not notice it. But as technology keeps improving, Google's ability to detect these link farms will become more accurate and immediate.
Many link farms are penalized by google however, the level of penalty varies from one site to the other.
They do penalize link farms with over 100 links on a page. If you have under that you are not penalized but the PR of that page will not be very high no matter how many backlinks it has