Google announced recently that it is making all seven of its popular and powerful Nik plugins available for free! I haven’t tried them all, but I love their U-Point technology for making local corrections, and I was really impressed by how I could easily produce stunning black and whites with Silver Effects Pro (that I didn’t have the experience to imagine beforehand.)
It appears from Google’s statement that they will be focusing on mobile applications going forward – so don’t count on future support for or development of these desktop plugins.
Update: if you’re looking for training on using Nik plugins, Tim Grey has a free video course.
Update: I am not a Nik expert and can’t provide troubleshooting help. Please check the troubleshooting section of the Nik site, or post in one of the Lightroom or Photoshop forums.