OhDearNigel A year ago I would have completely agreed with you. I though MIL was loopy putting DD on the potty at nappy changes when she was looking after her as I didn't see the point of starting "before the child is ready". However, having seen how the nurseries here and friends have tackled toilet training, I would probably choose to start much earlier if I have another child.
My experience with DD has not meant lots of wee on the carpet/floor. Although I took her out of nappies before she starting announcing the need to wee, she was accident-free most days from the start, simply by taking her regularly and watching her body language. She was, however, already able to wee on cue on the potty thanks to the nursery training.
Accidents in any case are almost always completely contained within her pants and trousers, so I only have had to wipe up puddles when she has been wearing tights. I can't actually remember the last full-on accident she had anyway, she sometimes dribbles a bit when she doesn't want to acknowledge the need to go and then waits to do the rest on the potty/toilet. I can imagine, though, the amount a child wees differs a lot from child to child and that summer clothes wouldn't soak up as much as winter ones.
Several posters seem quite scathing about taking the child regularly to the loo. I just want to point out that, even with a completely reliably trained child, you still end up encouraging them to use the loo before car journeys, before going out, before bed, etc.