I have to admit that I don't understand the point behind this tool, but podcasters way smarter than me have developed it and told me that it's needed so it must be.
The GigaVox team developed The Levelator in house to combat the problem of unlike volume levels in podcasts. We've all seen and lived through telephone interviews and conference calls where some people are much louder than others. If you use a recording solution where every participant ends up on their own audio track then normalizing all of them is trivial. I think the Levelator is aimed more at the situation where you have big audio differences on the same track.
To date, the normalize filter in Audacity has worked fine for me, but since the Levelator is free I'll be trying it out. Oh wait, no I won' t because there's only a Windows and OS X version. Maybe some other time, then.
The Levelator is supposed to be available from GigaVox as of yesterday, but I don't see it there yet. Maybe check back tomorrow.