I was in Dixons in Jervis Centre one day, and got so p**d off waiting to talk to someone that I rang 11850, loudly requested the HN Airside number, and phoned them from Dixons. I was able to do a deal with HN - if they did the same telly for 50 euro less, I would travel out to them. We left Dixons still not having been served or spoken to anyone in the place, and got about 80 euro off the HN price ... well worth the trip.
Did something similar with a washer, bought shop floor model, about 70 euro off, plus free delivery the following evening.
I never managed to get a single euro off furniture though, aside from this 10% Amex offer.