Notifying customers of upstream modifications

Hi All, Just a quick question for those of you running ISPs with BGP downstreams. If you add or remove an upstream provider to your network, do you provide notification to your downstream customers? Likely, it would cause a shift in their traffic. If they are peering with multiple ISPs themselves, they may see a traffic flux. I know for a fact that our upstreams do not notify us of events so we tend to not send out these sort of notifications. Just wonder what everyone else does or if anyone happens to know "best practice" Thanks, Andy