Search:

EMD update create lots of problem and derank most of the site which are just using the benefit of having great domain name in ranking.

If you are creating content for search engine point of view than this content never able to please the visitor of the site. You always need to think about user and than need to write best content...

Google Penguin is algorithm update which released to fight spam sites and remove them or derank them from search result.

Today's time most of the email marketing plans looks spam in the eyes of user. If you have quality website with lots of subscribers than it would be successful to run email marketing.

I think 2% to 3% is best for any kind of content. Using more than this would look like keyword stuffing and your site might get banned from search engine.

Obviously google is more popular because it providing better result to user than other search engine. Google update its search engine algorithm every few months for better search result.

Good and working sites but all of this sites are 0 PR and domain is also .TK. Still I would use this sites if this site has good domain authority otherwise using this site is not a good idea.