There is also now a "Bio-thermal" microchip availiable which as well as
containing a unique number to your pet, also displays its temperature,
eliminating the need for a rectal thermometer.  This one costs about £30
in England.  I also think microchipping is a MUST regardless of whether
your cat is an indoor or outdoor pet, as you never know whether they may
escape or be let out in a burglary.  Chipping over here is also cheaper
if done at the time of neutering.

My cats do not appear bothered. Their collars bother them, but not
their microchips. Now, inserting the microchip bothered them. That is a
*big* needle! But not the microchip itself.

My cats however were full grown fat moggies and had plenty of loose
skin and fat to place the microchip in. A leaner breed like a Siamese
might have more of an issue.

- Elron