I think they are handy where lots of people need boiling water and a kettle might not hold enough / cause trailing flex hazards / accidentally not get filled and switched on so wasting half your break waitiing for the kettle to boil.
Tony, the ones I've seen are a box on the wall with an urn-type tap. Unlike an urn they don't store up water, heat it then dispense it, they do it 'on demand'.
Most school staffrooms now have them, for the above-mentioned reasons of speed, safety, and preventing fist-fights breaking out when the last cup gets taken before I get there.
Many youth hostels have access to instant hot water. I believe there are a number of instances where people have got scalded with them. Because of worktop access think carefully if young children are around.
That's the problem with the one we have at work, Ginge... we are in a hard water area and despite having a dedicated water softener (obviously not a salt based one) for the tap it just scales up constantly. I guess for people in soft water areas they would probably be more reliable.
Thanks for all your replies. I shall look up quooker to see if it's what I'm thinking of but ones I have looked at so far are around £300. Just fancied a gadget in my new kitchen, which won't happen for sometime but it's nice to imagine. Also it may stop mr f filling the kettle to the brim for one cuppa