DNS explained - The Domain Name Servers by Indichosts.net: "Here is another example:
A friend or associate of yours can somehow see your new website and you can not. This is most likely because his ISP's DNS servers are able to get the information at that time, where your ISP's DNS servers can not. Huh?!?
Here is yet another example:
What if you inadvertently provide the wrong nameserver information to your registrar such as entering one DNS server correctly but the other wrong? In this case, you would have experienced these problems right up to and well beyond the 72 hour propagation period. You'll have to update that information again and wait another 72 hours. Ouch!
Here is a neat one:
You are transferring your hosting to a new WHP. During propagation you are working on development of some pages in your website. But you notice that when trying to view your most recent changes, they appear and then vanish or they don't appear at all."
'via Blog this'