Actually, although Supercool has attempted to put the record straight this is not the correct answer either.
You'd have to work with them all the time as I do to know what I mean and I'd need to write a book to put it all in, but in general they are a strong minded breed and they need to be raised correctly for sure. But, underneath is genetics and rottweilers can be born from one end of the scale to the other in drive and temperament. They can be laid back or hyper high drive. They can also be dog / dog aggressive if not socialised properly. Whatever their temperament and drive they must be raised well and they need years of training and socialising for sure. They are not a dog to just be left in someone's garden / yard otherwise you will have a dog that is trouble.
Here's a good article on whether you should buy a rottweiler or not and in reading that it tells you a lot about them.
http://www.dogwoodrottweilerclub.com/soyouwanttobuyarottweiler.asp
I had 25 rottweilers in my class yesterday... too many... but lots turned up as it was Christmas week and we have fun and games.