I'll be using Eibach Sportlines (with the appropriate dampers), which'll take it down between 45 and 50mm at the front, 25 and 30mm at the rear. Think that's about as low as I could go, but the roads/speedbumps around where I live shouldn't pose that much of an issue. Got some mates with cars lowered to that degree that never have an issue.
Yes really, perhaps you can take a few pics of the 'scrape free' underside of your car next time it's on a ramp! There are some speed bumps around here that no matter how slow, fast you go, you hit. If you have a couple of passengers and anything in the boot forget it. I spoke to a guy I met recently at a Fiat Dealer and the exact same happened to his as well, so maybe you have a 'special' one
Lowering a standard car shouldn't give you any problems at all, they only come when you've a body kit fitted, mine was lowered 35mm and was headache enough....