Has anyone got any good pointers for information on the hybrid effects achieved by grafting? Or personal experiences with it, for that matter?

I'd quite like to find some modern references on the techniques. I also have some red apple scions grafted to a variety of trees as of this year, and will be looking to see if there is any difference in the resulting fruit - for instance, whether the scion grafted to the granny smith tastes more tart than the scion grafted to the monty's surprise. Or whether the granny smith graft consistently loses the red colour in the produced fruit from the grafted scion.

Case 1: Someone was describing a tree their family had, which they wanted to propagate. The problem was that it was a pear grafted to an apple rootstock, and it had produced a unique apple-like pear graft hybrid. They weren't sure about whether they could safely graft a scion, and expect it to produce the same fruit.

Case 2: An 1830 report about someone grafting peach to almond to peach, and consistently getting oval shaped fruit, except where the graft failed and the almond was not involved, where they got standard fruit.

Case 3: An 1886 report about someone who grafted a desired variety and found that the qualities of the fruit of the scions differed depending on the qualities of the tree grafted to.

Case 4: The previous 1886 report, which also details the practice of grafting "in and in". The idea is that you take a scion of one variety and graft it to a tree of another, where both varieties are different, yet have appealing characteristics. Perhaps just red colour. Then you take the growth from that scion, and graft it back on to the tree you just cut it from, and repeat until the characteristics you wish enhanced, are suitably so. This is also elsewhere referred to as an old french technique.

EDIT: A link to a recent article in Nature, which gives some substantiation to graft hybrids, as a contrast to the older reports.