Moving to a new web site structure?

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

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  Jim Munro: If the old urls are 404, they will drop from the index and you will have to wait until the new urls begin to appear. You should 301 the old urls to the new urls. It`s not too late to start now.
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  Erik Deckers: Did you do 301 redirects on your old URLs?
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  Nishant Desai: If the urls are changed, you will have to do 301 redirects as suggested by Erik or de-list the old URLs and wait for the new ones to get crawled by google.
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  Per Jacobsen: Agree with the comments above. Hurry up and implement 301 redirects from all pages on the old site with good links and/or traffic - but only if you can 301 redirect to a similar page on the new site. You shouldn`t 301 all pages to the new front page for instance… It would of course have been best if the 301s were in place when you launched the new site, but fixing it now is better than never!