New iMac

We had a quick look at the new 27in iMac the other day and were most impressed with the display - very clear and not as intimidating as I feared. The magic mouse felt good too, and the keyboard was okay - what there is of it.
As always the Apple Store offers various customisation options which only serve to aggravate my normal indecisiveness. Has anybody got any opinions / experience / advice on choice of model and specification?
Trevor