As an en-route controller we try our best to relay the information to pilots but we don't always have all of the information. I realise that in the flightdeck you don't always know if you talking to terminal or en-route so understandably it can be frustrating.
Yesterday morning was interesting for us on Clacton (sector for the LAM arrivals) with delays reaching 35 mins yet the controller info screen was being updated with EATs only every 10 mins, hardly any aircraft in the hold at LAM (so we can guess at the delays) and not much info forthcoming from TC (not a bash, you guys have other things to worry about).
Our primary trigger for slowing aircraft down with us and also with Maastricht was the fact that we could see the ground speed of aircraft transferred to TC slowing dramatically, not the most scientific but it worked! Oh and once the published landing rate drops below 38 an hour we are always prepared for delays.
The LASs are good on B (Green) watch with regard to EATs from their more accurate machine. We try to give accurate delay info on first contact but it often more of an educated guess until we see the EATs appear (eventually!)