Great hack, like the others I am from the UK so having a few problems however I can pin point the road which is good enough for now
[map]Bletcham Way,Milton Keynes,Buckshire,MK78HP[/map] worked for me!
One other thing I noticed is that if I goto http://api.local.yahoo.com/MapsService/V1/geocode?appid=YahooDemo&location=<texthere> and enter a UK postcode in place of <texthere> it actually returns a result is it possible to have it work from just entering a postcode?