Are multiple domains targeting keywords a good plan?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  David Gemma: This is my web url - webdesignkent (dot) co and My targeted kw is web design kent and web design sittingbourne, I did on page and off page SEO for this site but when I have searched in google (dot) co (dot) uk there I have seen my url is not present in top 300 position. Another matter is when I have been searching for web design Sittingbourne on google (dot) co (dot) uk there I have found my other site url dancinggemssittingbourne (dot) co (dot) uk in 58 position but my question is why Its appeared into google (dot) co (dot) uk when I have searched for web design sittingbourne. Please someone suggest me what's going on to my sites or What would be my next footstep?
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  Dave Elliott: Really strange. I can't see anything wrong with that site. It Seems to well optimised.
  Unless Google webmaster tools is telling you you have a lot of crawl errors and have been hit with a penalty then I am stumped.
  
  Your home page title tag comes accross as a little spammy but i really cant see google punishing you for it.
  
  Did you recently purchase the domain? i'm wondering if it had previously been penalised or something
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  David Gemma: Hello Dave, this site is not penalized by Google webmaster tools. Also Thanks For your query.
  
  +Dave Elliott
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  Pe lagic: EMD with a totally unnatural link profile ;(
  
  ps You will get better results with a single branded site  ;(boomsolutions dot co dot uk)