The last time I moved a domain to a new host, I changed the nameservers with the registrar, waited a day or two, then went happily to work on the new website. I didn’t notice (until the bill came) that the previous host was still charging me.
So this time, I changed the nameservers and dropped an email to the previous host telling them that I had done so. They <sarcasm>very kindly</sarcasm> suspended the web hosting service immediately, way before the nameserver change propagated. So now my users are up the creek for a day or two. It’s my own stupid fault, though.