Question about 404 pages after server upgrade

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

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  David Mason: So, I'm having a minor panic attack because I just upgraded from a shared server to a VPS, and now I wait. I didn't consider that the site would be "down" for up to 12 hours. The server is working just fine, but anyone--Google especially--will be fed a bunch of 404s. Should I be concerned? As soon as DNS propgation completes, I'll be ready to migrate my WP site from my dev site to my shiny new VPS site. Any thoughts??? Any risk of SEO damage, here?
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  David Mason: Aw, man. I'm all good. Up and running. Woot, woot. Whew...
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  Jim Munro: I'd expect an increase due to improved performance, Paul but dns propagation is a term used by lazy sysadmins and larger registrars to explain their inefficiency and cost-reduction. Who manages your dns?
  
  What they are really saying here is that they only update their records once a day or every twelve hours but, if you have direct access to your nameservers and can change records, you should be able to see propagation within the record's Time To Live, usually one hour.
  
  Here is a useful tool to watch propagation with. ;https://www.whatsmydns.net/
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  David Mason: Thanks! Site is going hot. Pumped. You guys are a great community.
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  john ryan pagulayan: true +Jim Munro
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  Nick Fitzgerald: +Jim Munro is right. Good luck!
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  Joshua Berg: +David Mason if it's within a few days site ranking will usually not be affected, so usually wouldn't worry about this. If you go over 4 days to a week, then there's a possibility you'll see some temporary ranking drop.
  
  It especially depends how frequently your site was being crawled. If your site was being crawled daily, because you put up fresh content everyday, then the crawlers would catch onto the problem faster.
  
  But if you typically only had weekly, or monthly fresh content, then you might be on a weekly, or monthly crawl schedule & the spiders may not even notice that it's down. So in this case you'd fair better if your site was infrequently crawled.
  
  +Jim Munro is right about the nameservers, sometimes it can happen quite quickly.
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  David Mason: Thanks +Joshua Berg 
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  David Mason: Just thought I'd mention that the migration went off nearly wihtout a hitch. Thanks to all of you for your help and advice. Great community.