I'm lucky, mine is fitted with a keyless ignition. Sadly, he is also fitted with an immobiliser that seems to kick in at random sometimes

Seriously though, Chrissie started this thread a short while ago
http://www.enlightenedequitation.com/ee/boards/index.php/topic,44234.msg581634.html#msg581634that brought all sorts of useful ideas together.
I tend to follow the same pattern with any horse, but what varies wildly is the timescale, both overall and on each phase or activity. I think backing is a process that begins at birth and continues. I don't think the actual "sitting on top" bit should be a big event at all, but more just the next obvious small step that follows on from what they already know and are comfortable with.
So for example, Orio is two. He is well handled and works free in a school from hand and voice signals. It's all a big game to him

He will walk and trot on command and is learning "big trot" which we ask for when we show in hand anyway (and it's not as big as he is easily capable of, he's sadly limited by his asthmatic and slightly lame mother!!

). He also works nicely in hand, just off a headcollar, stepping forwards away from a driving body position, and he does basic shoulder-in in a headcollar from a hand aid. I haven't lunged him as such, but he does know how to circle on the end of my long rope and will walk and halt from voice commands. I only ever 'work' him for ten minutes at a time. He is a bright and well adjusted little chap and loves to come in to play in the school once every ten days or so. He's worn numnahs and surcingles, a variety of rugs, has had my saddle plonked on him loose in the field (he used to carry it in from the car for me as a yearling

), and is accustomed to having me on both sides, above him, round his bum, under his chest, arms on both sides hugging his barrel, all sorts. So he is unflapped by any weirdness I choose to throw at him
I will continue this sort or 'work' until he is rising four, adding in more formal in hand work and liberty work, and adding in a saddle and bridle eventually, then I'll put weight on him. I don't expect he'll find any of it remotely surprising!