One of the best parts of the FAQ explains this, starting right here and ending at the bottom of the page.

In short, don't worry about normalazation that much, and use VolAdj, part of the reason Hijack exists in the first place.

Perhaps it's a US/UK thing, but I find unnormalised CDs are much more common than the FAQ makes out. I appreciate the point of the FAQ entry that linear normalisation doesn't always solve the problem completely, but anything you can do to mitigate it at rip time rather than playback time is a good idea, as it will provide improvements when (sacrilege!) you use those MP3s not in a car player -- for instance, in your Receiver or your Ipod.

Peter