Well, I picked up my replacement the following Tuesday - still had a bleed issue in one corner but I thought I would use it to see if it bothered me it did. Although it seemed to be less than the previous unit, the severity of the bleed seemed to be vary a lot more depending on the angle, so when moving the iPad around (e.g. playing a game).Went to my appointment . They didn't have the same model in black and in stock, so was offered white then and there or to wait for new stock - I'm going to wait. Have to say, the customer service that I got was great, simply great.
Got another Apple Store appointment and although I got the resolution I wanted (i.e. it would be replaced), the customer service I got from the Genius was considerably less impressive than last time - e.g. when he offered a replacement, he said that as it's a new product, there would be no guarantee that it would be better.
Anyway, picked a new unit up the following Tuesday - this time, it was brown box replacement, so they just swapped the iPad. This one is great - although I would say that in very dark conditions and at higher brightness, there is very slight bleed, these are not conditions I would be normally using the iPad and I was really only able to notice it when I was looking for the problem.