There are several ways to deal with this 'problem'. I read an article about editing the stylesheets, masterpages and so on.
I also saw a post about using a content editor webpart, which is close to the way I am dealing with this issue. I uses a webpart and actually I don't know who's created this one, but it works fine.
It is the 'HideQuickLaunch' webpart.
Add this web part to the site collection where you want use it and add this web part on that page/site you want to hide the Quick Launch bar. That's all.
You can download the dwp-file (zipped) here.