I have to say, I've yet to see any consequences of microchipping, and I've chipped hundreds of animals. As Wolfy said so succinctly, it's just a very high-tech ID tag. My kids are chipped, and I will continue to chip future ones until I see something more compelling than "1% of the mice chipped developed tumours somewhere on their bodies over the course of a year".

Considering that the technology has been out for a couple of decades, I'd expect to see better data.