Executive summary about the Sidi boots by Simon Bradley
You could do what most people did and wear the same boots you normally did, suffering cold, wet digits and taking a real risk of getting trench foot. You could improve things by sticking your foot inside a carrier bag before putting your boots on, possibly even attaching another carrier bag outside the boot with rubber bands.
So if you fell off, and, let's face it, if you were riding in the rain a few years ago the chances of falling off on your rubbish tyres were fairly high, then you were far more likely to break your foot. So most people just got wet feet.
Now since those dark days things have steadily improved, until today it's possible to buy purpose made motorcycle boots which are waterproof, comfortable and protective. Enter the Black Rain Evo (one of the Sidi boots). Cool name and boots.
You put them on, wear them, and treat them like normal boots. I rode in the rain, and didn't get wet feet. Because actually immersing a boot is a great way of testing it thoroughly. Now since I've had these boots I've done around 3000 miles in them. They're my normal footwear on the bike, unless I need to wear race boots. Although the boots seem to breathe, your feet will get quite warm when it's ninety degrees outside.