It's true that speed bumps are hard on under axle units, but unless you have combinations of:
1)
really low car
2) mountain high speed bumps
3) said mountain high bump on narrow path divided by a high curb/barrier
4) going over the bump straight (most common mistake)
5) fat friends or ...gasp...fat girlfriend
I've found a lot of times, if the car is lower than normal, and there is a speed bump, I can clear it without scraping, if you go over it "sideways"
As you approach the hump, you quickly turn the wheel so that you basically end up in the opposite lane when the one of rear wheels begin to catch on the bump.
Don't believe me? Give it a try the next time you're out driving late - and stop with the parking brake and take a look under the car. The key here is as sideways as possible and going slow.
Of course there will be times when you just cannot go over the bump sideways due to traffic and/or a narrow path... however, in the city where I'm from, I can clear them 90% of the time...