You cease your contract with your hosting company, cancel your contract and move your web site. People start to complain that they cannot reach your web site. Nothing seems out of order.
You were hosting with a major ISP (like Eircom, Magnet or BT Ireland). They put DNS entries into their servers for your web site. When you cancel your contract they should remove these entries. Magnet and BT Ireland are two companies that are negligent in this regard. If they don’t remove these DNS entries, then their customers can have problems reaching your new web site.
The bad & ugly:
BT Ireland and Magnet are two shining examples of neglect and incompetence. I came across two recent cases where hosting had been cancelled by a client but the hosting company did not remove DNS entries. The upshot was that their customers were having problems connecting to the client web site. This is quite difficult to detect: Unless you are using a connection supplied by the bad & ugly ISP, the chances are you won’t notice.
If you must host your web site with an ISP, host your DNS elsewhere. Without it your server effectively becomes invisible to your clients and you stop getting email. DNS is more than just finding your web site. It is used to find your mail servers and more.
There will be times when you need to change your web site address in a hurry. When that happens, you don’t want to be stuck with someone like BT Ireland (who insist that you fax a request on headed paper to them and tell you it will take 24 hours)!