HTB QoS for VoIP at sites with residential Internet connections that won't honour your markings

Do any of you guys implement HTB QoS for VoIP at your sites that have Internet feeds that aren't going to honour your markings?

Do you guys see any benefit for doing this or is it just a waste of time since the ISP isn't going to honour the markings? I would be marking the VoIP traffic and then putting them in a HTB priority queue.

IMO I see it being useful in a scenario where the sites WAN Upload is at 100% utilisation in which case the VoIP packets will be sent out the queue before everything else. I see it mainly being useful during 'bursts' of traffic not shown in SNMP polling intervals.

I would like to hear everyone else's thoughts on this.