Mega Menus effect on SEO

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

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  Dave Elliott: not convinced it will make any SEO differnce. As for HCI umm depends on how its done. something like ;http://www.dnnsoftware.com/ is clean and very easy to use. (even if the i really hate the logo!) Where as something like this ;http://www.homedepot.com/ is just plain rubbish, an narrow, and the footer is lame and..... its just an appalling website really.
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  Federico Sasso: When mega-menus took place about four years ago, usability guru Jacok Nielsen plauded their usability, at least compared to normal dropdown menus. Worth reading: ;http://www.nngroup.com/articles/mega-menus-work-well/
  
  From an SEO standpoint, they are pretty like normal dropdown menus: their weak point is adding too many links per page, flattening link structure and highly reducing the boost of deep links you want to promote from your home page.
  Nowadays simple tabbed menus with just 4-5 entries are usually preferred by SEOs for general navigation, but there are cases where rich menus are indeed useful, e.g. ecommerce sites. In such cases, I think mega menus improve navigation experience compared to dropdowns.
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  Carl Harvey: Good question and great answers...I've got menus down the side so time for a re-think now i suppose
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  Ian Dixon: Interesting that you mention Home Depot there +Dave Elliott ;because I've seen a few from the US refer to them as _Home  ;Despot.
  That Nielsen article is great though and was well worth looking at. Got me thinking some more about my own design styles. Thanks for the share with that one
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  Justin Y: I don't think using mega menu is a problem as long as the structure is good. I think the best thing would be to focus on the prime real estate in the menu and add the most important menu items starting from the top first. Push the least important menu items to the bottom of the menu.
  
  As for the SEO, I don't think it will hurt anything as long there are no duplicate links like in a sidebar nav or in footer of the website. If there are duplicate links, you might want to consider adding nofollow tags to any of the them that are global. These are my thoughts and what I normally do when dealing with large menus/mega menus.