Well im all for more choice in the serving sizes, in fact im all for complete deregulation in this area, but from the only place ive seen 2/3 introduced, it seems to have pushed up prices.
Beer 1 Jan 27 : £2 a 1/2 Feb 7 : 2.80 2/3 (£4 vs £4.20)
Beer 2 Nov 21 : £2.50 a 1/2 Feb 7 : £4 2/3 (£5 vs £6)
Beer 3 Nov 21 : 2.50 a 1/2 Jan 27: £3.90 2/3 (£5 vs £5.85)
Maybe 2/3 glasses wasn't such a good idea after all.