A few days ago author, J.L. Langley, wrote about her experience with being plagiarized. So I link you to her Writing Update #9 and A Message From J.L. Langley which covers the incident from her point of view. Though it's near impossible to stop those who plagiarize from doing so, Ms. Langley has a lot of useful information to share about protecting your work and being able to prove that it is yours.
I know other authors have experienced this as well. Jordan Castillo Price is one who comes to mind and gave me lots of fantastic advice and information about how to handle situations like this. You can read about JCP's experience in 2009 here.
I suppose this is on my mind at the moment as I get to the end of Scholar's Rock and realize how much I've put into this work. Not just time, but emotional, mental, and physical exertion. Writing is joyous and fulfilling. I wouldn't want to be doing anything else. The thought that someone would take another person's work and claim it as their own is disheartening. The reality of going through this situation is a nightmare that takes up time and more emotional exertion.
Thankfully, both of these incidents ended up in victory for the original authors.