I have backed up my files to disc, memory sticks and hard drives.
In 2010 I registered a rough draft of my novel and future ideas, in the UK with
http://www.copyrightservice.co.uk/
In 2013 I registered my novel and future ideas, in the USA with
http://www.copyright.gov/
Adrian, how would it work if someone comes up with a similar idea to yours on their own? If they haven't seen your work but have simply thought along similar lines. None of us create in a vacuum and, while we each bring our own voice to our work it can happen that two people who are completely unrelated come up with similar concepts. Just a thought. Hope it doesn't happen to any of us!
Andrew, what I mean by ideas is rough outlines of future novels. Plots, storylines, characters, working chapter titles etc. A sort of synopsis with notes. I have done this for three future novels in a series.
They may not be written for years. But I'll have proof if someone writes something similar in the meantime.
There are always people who will copy others' work if they get the chance; the internet is awash with copied material. I agree that it is vital to back up your written work, on another disc, memory stick, hard copy or whatever (all of them i you are so minded). However, if you are worried about your written work being copied, surely the best thing is not to put it out there until it is finished and published in print or digital form. Thereafter, your redress for plagiarism is the law.
I'm puzzled by how one can register ideas and why one would want to. Ideas do not have physical form and are not protected by copyright.