It's all in the resolution, DG. 'HD Ready' is usually up to 720p resolution (1280×720), whereas Full HD is 1080p resolution (1920×1080). An 'HD Ready' set will usually accept the higher resolution input from, say, a Bluray player, but will downscale the output to it's native resolution, which, I think, to be precise, is usually 1366x768. A 'Full HD' set will display the picture at the full 1920x1080 resolution, hence, theoretically, a sharper image.
Some people are more decisive than others Simon.
How much did you pay for yours, Dave? The cheapest I can find is at Marks & Sparks for £650. His Lordship is talking about buying one tomorrow.
I've been scouring the net and apparently Amazon are doing the 40" set for £599. I found a discount voucher which will supposedly get a further 10% off.