What effect do inpage links have on SEO?

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

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  Tony McCreath: Search engines index them all under the one page without the anchor text (#) so no issues using them.
  
  In some lucky cases you may get a bonus "jump link" in your search result snippet letting people go straight to that anchor.
  
  There is a special case called the hash bang (#!). This is a hack supported by the search engines to help them crawl ajax websites.
  
  One negative is that I've seen some social buttons consider the anchored link as a separate page and split the social count up. I'd consider that more of a bug on their account.
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  Devin Peterson: Another question, when setting the id="name", do I have to declare that id in the css file? And should I use keywords or can i use generic tags like "#nav1" or "#section2" ?
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  Justin Y: +Devin Peterson no you don't have to unless you plan on adding custom styling. You can call the ID's whatever you want, I usually create the ID based on the main keyword for the section I want the link to jump to.
  
  Dogs
  id="dogs"
  
  Another alternative is to use javascript scroll or Jquery to achieve a smooth transition in between content. Either way I don't think there's any value other than user experience on whatever route you choose.
  
  
• 
  Tony McCreath: For compatibility I would set up both id and name to the same value. In the past different browsers supported different attributes.
  
  I'd use keywords just to make the URLs look nice.
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  Justin Y: +Tony McCreath Tony you're referring to html vs html5 correct?
• 
  Tony McCreath: +Justin Y ;Pre html5 issues. I wrote a simple article in my early days (2010) where I noted it was an issue:
  
  http://seo-website-designer.com/Page-Anchor-Links
  
  We may be in the clear now.
• 
  W.E. Jonk: Make sure the hash URL's have a rel canonical to the canonical URL (without hash). Maybe Googlebot understands it but social buttons like the plus one don't. And there is no way to transfer them (or at least the count will not be transferred).
  
  Reference :D: https://plus.google.com/u/0/107268296166433236059/posts/Xm6UfW2MzYd
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  Devin Peterson: Thank you everyone. This clears it up!
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  Tony McCreath: +W.E. Jonk good point. Many social buttons also have ways to state the url for the button which also stops those sort of canonical share issues.