such rankings drops are generally temporary. wait for few more days. How soon you will recover your rankings depends upon how frequently Google crawl and index your website.

Did you change the title tags of some of the pages knowingly or unknowingly? This could be one of the main reason. Other reasons can be accidental changes in the robots.txt file, htaccess file or incorrectly placed rel=canonical, meta noindex tags on certain pages. There is also a possibility that your website is hit by recent Penguin update or for over optimization. You need to check your website against all of these possibilities.

Google can index URLs up to 2047 characters in length. You will receive a 414 error if you exceed 2047 character limit.

http://productforums.google.com/forum/#!category-topic/webmasters/crawling-indexing--ranking/h0aeO2_kpac

Google can determine the screen resolution your website supports and can then calculate the contents above the fold through some predefined criteria. So it has nothing to do with the screen resolution of the end user. To better understand how Google do this, check the browser size tool in Google labs. The concept of above the fold used by Google is to actually filter out those web pages on which ads outweigh the contents as it leads to poor user expedience..

Google wont penalize you for duplicate web design. But it does look at the layout of a web page to check how much content is above the fold using page layout algorithm. So while designing a layout make sure that you have considerable amount of contents above the fold. Web design doesn't effect ranking position directly but indirectly it can effect because of high bounce rate and other user metrics.

You wont be penalised for such type of redirect. You can block all the traffic coming from their domain or IP via .htaccess file.

At the end of each blog post/article remind your readers to follow you on twitter. This work wonders. Another cool way is to pay by tweets. If you provide a downloadable resource on your website, then make it available only after tweeting about it. Make sure that your twitter button recommends to follow you, if a visitors is not already following you. With the passage of time you will get many followers.

When did you make changes to the title tag? The new title tag will appear in the SERP only when the page is re-indexed by Google.