I saw many website especially blogs nowadays copy other sources' content and rewrite it to be they own content. Of course, they include the source in the bottom of their posts. This kind of blogs have high pagerank too! Is this legal? Are the rewritten content be considered unique content?
In all honestly rewriting someone elses work is against the law. However, in reality it is done everyday on the net. Using others work as long as you have permission and give the credit according to that authors requirements is acceptable. Many webmasters find filler articles from sites such as Ezinearticles.com and others like it. While you will never be ranked as high in the serps as the original site that posts it these articles can help fill voids you might have. The best route is to try and come up with your own original articles as you will be most rewarded from well written articles that are interesting and informative.
Nowadays, you can see many tech & gadget blogs out there, most of the time, all these blogs report on the same topic/news. So, I plan to start a blog like this because AdSense pays very high on these keywords.
IMO, rephrased it and make it different, but not to run out of the topic, that's the best, else, it will enhance your writing and grammar experience.