Anytime you duplicate content from another web page then yes your SEO is and will be negatively affected.
Creating your own and Unique content is much better than copying and pasting one. Remember there is a law about Plagiarism, having a unique content can be very beneficial for you, try to make an informative one people now a days are looking for such informative articles or post this can help you to drive a lot of traffic to your site. if you are not that good in writing you can re phrase such contents
Duplicated content will only harm your ranking of your site, but not improving it. Where did you hear that from?
Its all rumours. This forum is full of people who don't know what they are talking about yet they still give advice thinking they are being helpful when really they are being the opposite.
When copying content to some web 2.0 sites will include everything like tables, images, and i don't think that's cool.
General speaking, copying and pasting content have negative effects for seo . If you have good way to avoid google discovering your tricks, it helps a little . lol But anyway don't make evil .
Copy paste could lead to duplicate content. Duplicate pages are often removed from search engine index as not useful. So yes it is possible that copypaste could affect the seo results, even remove a page from the index. I recommend you to check your pages with a tool and see how relative they are. You can find such a tool here: http://www.webseoanalytics.com/free/seo-tools/duplicate-content-checker.php
Why even try copying content? I don't understand. You can take content and go to elance's website or "need an article" website and have someone rewrite it for very little money and you wouldn't have to worry about it in the first place. You can get a 1000 word article rewritten for $10 so why would anyone risk getting a good ranking in the first place.